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Infection, Immunity 

AND 

Serum Therapy 



In Relation to the Infectious Diseases 
of Man 



H. T. Ricketts, M.D. 

LATE ASSISTANT PROFESSOR OF PATHOLOGY, UNIVERSITY OF CHICAGO 



SECOND EDITION 

Revised and Enlarged by the Author and by Geo. F. Dick, M.D., 

Instructor in Pathology, University of Chicago, with 

Preface by Ludvig Hektoen, M.D 



CHICAGO 

American Medical Association Press 

535 dearborn avenue 

i9'3 



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o xx 






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Copyright,, 1913 
the American Medical Association 






©CIA346383 



"PREFACE TO THE SECOND EDITION 



The circumstances that led to the first publica- 
tion of this book as well as its general scope and 
character are explained fully by Dr. Eicketts in 
the preface to the first edition. The book met 
with such favorable reception that the edition was 
exhausted while the demand continued active. 
This indicated that an actual want had been met 
and so it was determined to publish a new edition, 
revised and enlarged, and for some time previous 
to his greatly lamented and untimely death Dr. 
Ricketts gave freely of his already heavily taxed 
energies and strength to the work of revision. 

Surely a simple word or two in tribute to the 
memory and achievements of Dr. Eicketts are not 
out of place at this point. He died in Mexico City., 
May 3, 1910, at the age of 39, from typhus fever 
which he was investigating with splendid success; 
when he was taken ill. Thus a noble and inspiring 
career of large service to humanity and of rich 
promise came to a sudden and heroic end. During 
his short but intensely active life as an investi- 
gator in the field of infectious diseases Dr. Eick- 
etts made important contributions of permanent 
value to medical science : he greatly advanced our 
knowledge of blastomycosis; he solved the most 
important problems in the cause and transmission 
of Eocky Mountain spotted fever, and discovered 
that this disease is conveyed by a tick (Derma- 
centor venustus and D. modestus), in which the 



iv PREFACE TO THE SECOXD EDITIOX. 

infection is hereditary, thereby enlarging our 
understanding of the part insects may take as 
carriers of disease; he demonstrated that the 
typhus fever of the Mexican plateau, tabardillo, is 
carried by the body louse (Pedicuhis vestimenti). 
and the results of his work on this disease, which 
he had only just begun, will be of fundamental 
significance in its prevention and in all future 
investigation as to its cause and nature. In his 
death "on the firing line" we lost an investigator 
of the first rank whose name through these achieve- 
ments will live in the history of medical science. 

When the papers and manuscripts left by Dr. 
Eicketts came to be examined it was found that 
while the work of revision and enlargement of this 
book was very far from complete yet he had car- 
ried it so far that it seemed unwise not to attempt 
to carry it through to completion. Fortunately 
Dr. George F. Dick was willing to take up the 
unfinished task, which proved to be a much larger 
one than was anticipated for the reason that, in 
addition to completing the revision and adding a 
considerable amount of new material, it was neces- 
sary also to secure proper coordination and balance 
between the different parts of the book. 

The book is now divided into an introduction 
and three parts instead of two as in the first edi- 
tion. The Introduction and Part I were prepared 
by Dr. Eicketts and the chapters on "Sources of 
Pathogenic Micro-organisms*' and on "Special 
Features of Infection" are new. Part II contains 
new chapters on "Complement-Deviation." "Opso- 
nins," and "Anaphylaxis," and Part III chapters 
on "Epidemic Poliomyelitis," "Xoma," and "Kala- 
Azar," all by Dr. Dick. The old chapters in Parts 



PREFACE TO THE SECOND EDITION. v 

II and III have been revised by Dr. Dick in the 
light of recent work and some of them largely or 
wholly rewritten, notably those on "Syphilis" and 
"Spotted Fever." As a result the size of the book 
has been increased nearly 200 pages. It has been 
the aim throughout to follow the lines laid down 
by Dr. Eicketts in order to secure an adequate 
presentation, suitable for physicians in general, 
of the large subjects of infection and immunity 
as illustrated by the human infectious diseases in 
the light of modern knowledge. The present 
intense and widely spread activity of investigation 
in these fields, with its many discoveries, is giving 
us new principles and methods of treatment, cura- 
tive as well as preventive, and of diagnosis, which 
require a thorough mastery by the physician in 
order that they may be used to the best advantage. 
It is my belief that this book by Dr. Eicketts as 
revised and enlarged by himself and Dr. Dick will 
be of real service to the physician who desires a 
reliable guide to a helpful understanding of the 
subjects with which it deals. May the use to 
which it is put show that the labor expended on 
it shall not have been in vain. 

Ludvig Hektoex. 
Chicago, May 5. 1911. 



"PREFACE TO THE FIRST EDITION 



Immunity, in its present state of development, 
with its manifold new terms and special methods 
of experimentation, is a subject which appears 
difficult to one who has not studied the newer 
literature assiduously and grown into a knowledge 
of the conditions through actual work in the lab- 
oratory. Much of the literature is technical in 
character and appears in journals not commonly 
found in the hands of the physician and student. 
Much of it also is comparatively recent, and its 
"essence" has not yet appeared in books which are 
in general use. The literature of immunity, more- 
over, grows so amazingly that the analysis even of 
current works is a task of no mean proportions. 

At the same time, the subject is one of great 
interest and importance, and there exists a gen- 
eral wish, frequently expressed, to know more 
about the recent advances and the conditions which 
have operated against the success of serum therapy 
on a broader scale. 

The editor of The Journal of the American 
Medical Association, appreciating the need which 
seemed to exist, requested me to prepare a series 
of articles on the subject of "Immunity," which 
should present the general . principles and the 
important theories and facts, in as simple a man- 
ner as possible. These articles appeared from week 
to week during 1905 in The Journal of the Amer- 
ican Medical Association, and after revision, and 



viii PREFACE TO THE FIRST EDITION. 

with such additions as would contribute to the 
completeness of the work, they are now collected, 
in larger type, in the present volume and under a 
more suitable title. 

It was thought best to treat the subject broadly, 
to begin with the fundamental principles of infec- 
tion and resistance and to introduce the reader to 
the more complex conceptions of the present time 
by taking him briefly over the main historical and 
developmental steps. 

It will be obvious that the views of Ehrlich, 
concerning the production of antibodies, the nature 
of the reactions into which the latter enter, and the 
methods by which bacteria produce disease, have 
been utilized extensively. This course demands no 
justification, when it is appreciated that by no 
other means can one at the present time correlate 
a multitude of well-established facts which bear 
on the problems of immunity. Whatever may be 
the eventual fate of the side-chain theory — and 
certain phases of it carry the aspect of finality — we 
should appreciate as much as possible the extent to 
which it has shaped modern thought, and recognize 
that it has won an imperishable place in the his- 
tory of biologic progress. 

It should also be understood that the utilization 
of the side-chain theory in no sense carries with it 
a negation of the importance of phagocytosis, a 
fact which is plainly set forth on pages 356-7. 
Without doubt the role of the phagocytes in recov- 
ery from a large group of infections is on a better 
and truer basis than it has ever been before, and 
for this condition the recent work on opsonins has 
been most significant. 



PREFACE TO TEE FIRST EDITION. ix 

In relation to the grouping of the infectious 
diseases adopted in Part III, attention is called 
to the explanatory paragraph, page 398. 

It will be noted that a bibliography of the sub- 
ject of immunity has not been added, and this 
needs no explanation to one who is conscious of 
the massive proportions of the literature. A crit- 
ical analysis of the entire literature, which would 
not have been in harmony with the endeavor to 
present the topics briefly and clearly, and which 
Avould have made detailed references essential, has 
not been attempted. The most recent literature 
on the various subjects is accessible through the 
Index Medicus, or the index prepared semi- 
annually by The Journal of the American Medical 
Association. 

The index at the close of this volume serves as 
a glossary of terms, the explanations of which may 
be found on the pages referred to. 

H. T. Eicketts. 

Chicago, February, 1906. 



CONTENTS. 



Introduction: Historical and Developmental 
Data 1- 12 



PART ONE— PRINCIPLES OF INFECTION. 

Chapter I. 
Parasitism, Infectiousness, Contagiousness 13- 21 

Chapter II. 
Infectious Etiology 22- 32 

Chapter III. 
Infection Atria and the Excretion of Micro- 
organisms 33- 40 

Chapter IV. 
Sources of Pathogenic Micro-Organisms : 

1. Earth, Etc 41- 42 

2. Food Substances 42- 43 

3. Animals 43- 45 

4. Body Surfaces of the Individual 45- 46 

Chapter V. 
Sources of Pathogenic Micro-Organisms (con- 
tinued) : 

5. From Man to Man 47-63 

Chapter VI. 
Sources of Pathogenic Micro-Organisms (con- 
cluded) : 

6. Dissemination and Transmission by 

Insects : 

A. Dissemination 64- 67 

B. Transmission 67- 87 



xii CONTENTS. 

Chapter VII. 
Special Features of Infection: 

1. Virulence, Toxicity, Etc 88- 94 

2. Types of Infection 94-102 

3. Nature and Mechanism of Infection 102-127 



PART TWO. 

Chapter VIII. 
Types of Immunity 128-136 

Chapter IX. 
Natural Immunity 137 

1. Protection Afforded by the Body Surfaces. .137-143 

2. Internal Protective Agencies: 

A. Inflammation 143-149 

B. Properties of the Serum and Plasma. .149-160 

Chapter X. 
Acquired Immunity 161-175 

Chapter XI. 
Toxins and Antitoxins 176-190 

Chapter XII. 
The "Structure" of Toxins and Antitoxins and 

the Nature of the Toxin- Anti-Toxin Reaction. .191-205 

Chapter XIII. 

The Phenomenon of Agglutination 206-218 

Chapter XIV. 

The Nature of the Substances Concerned in 

Agglutination 219-233 

Chapter XV. 
Precipitins 234-244 

Chapter XVI. 

A. General Properties of Bactericidal Serums . . . 245-256 

B. Hemolysins 256-278 



CONTENTS. xiii 

Chapter XVII. 
Complement Deviation 279-291 

Chapter XVIII. 
Cytotoxins 292-305 

Chapter XIX. 
Phagocytosis 306-323 

Chapter XX. 
Opsonins 324-338 

Chapter XXI. 
The Side-Chain Theory of Ehrlich and Its Rela- 
tion to the Theory of Phagocytosis 339-361 

Chapter XXII. 
Principles of Serotherapy 362-380 

Chapter XXIII. 
Anaphylaxis 381-397 



PART THREE— SPECIAL. 

Chapter XXIV. 
Group I. — Diseases, Natural or Experimental, 
Caused by Soluble Toxins of Bacterial, Animal 
or Plant Origin: 
A. — Bacterial Diseases: 

Diphtheria 398-408 

Tetanus '. 408-419 

Botulism 419-422 

Bacillus Pyocyaneus 422-425 

Other Soluble Bacterial Toxins 425 

B. — Intoxication by Soluble Plant Toxins: 

Hay Fever 425-427 

Other Plant Toxins 427-428 

C — Intoxication by Soluble Animal Toxins: 

Poisoning by Snake Bites 428-431 

Other Zootoxins 431-432 



xiv CONTENTS. 

Chapter XXV. 
Geoup II. 
A. — The Serum in Acquired Immunity is Increased in 
Bactericidal and Opsonic Power: 

Typhoid Fever 433-449 

Paratyphoid Fever 449-453 

Acute Epidemic Dysentery 453-459 

Meat Poisoning by Bacillus Enteritidis 459-463 

Bacillus Coli 463-469 

Cholera 469-480 

Plague 481-492 

B. — Diseases in Which Acquired Immunity is Not Due 
to Increased Bactericidal Power of the Serum, or 
Knowledge on this Point is Deficient: 

Anthrax 492-498 

Malta Fever 498-500 

Chapter XXVI. 

Group III. — Acute Infections in Which Lasting 
Immunity is Not Established. 

Pneumococcus Infections — Pneumonia 501-515 

Streptococci 515-537 

Staphylococci 537-550 

Micrococcus Catarrhalis 550-551 

Gonorrhea and Other Infections with the Gono- 

coccus 551-556 

Epidemic Cerebrospinal Meningitis 556-563 

Influenza 563-569 

Soft Chancre 569-571 

Bacillus of Friedlander and Other Members of 

the Capsule-Forming Group 571-572 

Chapter XXVII. 

Group IV. — Chronic Infections in Which Lasting 

Immunity is Not Established. 

Tuberculosis 573-615 

Leprosy 615-623 

Glanders 623-629 

Rhinoscleroma 629 

Actinomycosis 629-633 



CONTENTS. xv 

Madura Foot 633-634 

Infections by Streptothrix, Cladothrix and 

Leptothrix 634-635 

Oidiomycosis 635-641 

Chapter XXVIII. 
Group V. — Diseases Due to Spirilla. 

Relapsing Fever 642-646 

Syphillis 646-652 

Frambesia " 652 

Other Spirochetes 653 

Chapter XXIX. 
Group VI. — Protozoon Infections. 

Malaria 654-670 

Trypanosomiasis 670-684 

Texas Fever 684-686 

Amebic Dysentery 686-690 

Sarcosporidia 690-691 

Balantidium Coli 691-692 

Cercomonas Intestinalis 692-693 

Trichomonas 693-694 

Coccidiosis 694-695 

Kala-Azar 696 

Chapter XXX. 

Group VII. — Diseases of Doubtful or Unknown 

Origin. 

Hydrophobia 697-710 

Yellow Fever 711-720 

"Spotted Fever" of the Rocky Mountain States . . 720-725 

Typhus Fever 725-728 

Dengue Fever 728-729 

Acute Articular Rheumatism 729 

Smallpox and Vaccinia. 729-743 

Chickenpox (Varicella ) 743-744 

Scarlet Fever 744-747 

Measles 747-750 

German Measles (Rotheln) 750 

Whooping - Cough 750-755 

Mumps 755-756 

Epidemic Poliomyelitis 756-758 

Noma 758-759 



INTRODUCTION 



HISTORICAL AND DEVELOPMENTAL. 

The conception of the nature of immunity Early Times 
which was current at one period or another of ti"esr rac " 
history had some relationship to the conception 
of the etiology of diseases at those times. It will 
be remembered that at one time diseases were 
supposed to be imposed by an angry deity,, and to 
avert them various mysticisms were resorted to, 
such as the utterance of incantations and the 
wearing of talismans. On the other hand, a more 
logical attempt to explain the natural immunity 
of the Psylli against snake poison was made by 
Pliny, who suggested that it might be due to their 
habit of drinking water from wells in which pois- 
onous snakes dwelt. This is not unlike our pres- 
ent conception of active immunization. 

Von Behring quotes literature to show that 
among some primitive races of to-day, artificial 
immunization is carried on; a Mozambique tribe 
is said to inoculate against snake poison by rub- 
bing into a small cutaneous incision a paste which 
contains venom. Probably non-fatal quantities 
are introduced in this way, resulting in the forma- 
tion of venom antitoxin, a method comparable to 
that used in the production of diphtheria anti- 
toxin. 

At a very early period the possibility of habitua- 
tion to poisonous drugs was recognized. We*learn 
that Mithridates by taking gradually increasing 
doses of poisons established in himself resistance 



2 INFECTION AND IMMUNITY. 

of this sort. It is stated also that he fed ducks 
with poisons and then proposed to use their blood 
as an antidote (serum therapy). The importance 
of antidotes in the minds of the ancients may be 
appreciated from the fact that epidemic diseases, 
such as plague, cholera and smallpox, were at one 
time considered as due to unknown poisons, which 
might be comparable in nature to some known 
poisons, as aconite. Mercury for syphilis, quinin 
for malaria, and salicylic acid for rheumatism 
would certainly have fallen into the category of 
antidotes, and mercury may have been so con- 
sidered. 

A historic illustration of the treatment of dis- 
ease on a supposed etiologic basis is found in a 
theory which was prevalent in the seventeenth 
century, according to which diseases were either 
acid or basic in character, and hence should be 
treated, the one with an alkali, the other with an 
acid. Sylvius considered plague to be of acid 
nature and administered alkalies, while Etmuller 
took the opposite view. 

Manifestly, rational treatment and prophylaxis 
of the infectious diseases could not be undertaken 
until their etiology was correctly understood. Yet 
here, as so often happens in medicine, empiricism 
preceded rationalism. For example, protective 
inoculation did not become a principle until the 
time of Pasteur, yet it had been practiced against 
smallpox for centuries, and the method put on 
its present basis by Jenner long before there was 
any idea as to the principles involved in the pro- 
tection. 
Micro- The belief that invisible "animalcules" are able 
to cause morbid processes in man is a very old 



organisms. 



THE MICROSCOPE. 3 

one. A passage from Varro (116-27 B. C.) reads 
as follows: "There are swampy places in which 
grow animals never so small which may not be 
recognized by the eye, and which gain access to the 
body through the air and bring about severe 
diseases/' 

The discovery and use of the compound micro- The 

n J . ., , t i n -i Microscope. 

scope m the seventeenth century disclosed tne 
reality of the minute living forms which had been 
suspected so often. Kircher, with his first crude 
microscope (1646), examined the tissues of va- 
rious diseases, and was the author of many the- 
ories as to their etiology. It is now believed that 
the magnification of Kircher's microscope was so 
small that many of the "worms" which he saw 
were really larger fungous cells and in some in- 
stances the as yet unidentified blood and pus cells. 
Leeuwenhoek (1632-1723), a Dutch naturalist, 
with his compound microscope magnifying 1,000 
diameters, observed accurately many microscopic 
forms, but made no application of his discoveries 
to medical problems; nevertheless, such applica- 
tion was not wanting, and the succeeding century 
and a half saw such voluminous descriptions of 
microbes, so many contradictory theories and 
statements concerning their relationship to in- 
fections, that the "infinitesimally small" fell into 
disfavor in many quarters as the causes of diseases. 
The attractions and reasonableness of the theory, 
however, were such that it continued to gain ex- 
ponents, and in the early part of the nineteenth 
century reached a degree of definiteness. In 1855, 
the great French physician, Bretonneau, affirmed 
that a specific germ was the cause of every con- 



4 INFECTION AND IMMUNITY. 

tagious disease: "An epidemic disease can orig- 
inate and extend only through the agency of the 
germ producing it." Yet at this time no infec- 
tion had been definitely proved to be of microbic 
origin. 
Anthrax. i n 1850 Eayer and Devaine made an observa- 
tion, which might have fallen into the oblivion of 
many preceding ones had it not been confirmed by 
later investigators. They found "small filiform 
bodies" in the blood of sheep which had died of 
anthrax, and were naturally inclined to believe 
that these forms caused the disease. Other scien- 
tists, especially Pasteur and Koch, soon took up 
the study of anthrax, with the result that the 
small rods of Devaine were scientifically proved to 
be its cause. 

Fermenta- Two great minds dominated medical research 
at this time — Pasteur and Koch. Pasteur, in his 
early career as a chemist, had had his attention 
called to the processes of fermentation. He re- 
curred to this subject at a time when the theory 
of the spontaneous generation of small living 
forms was widely discussed, and in 1857-1861 
proved beyond any possibility of doubt that lactic 
acid, alcoholic and butyric acid fermentations are 
due to the action of minute living cells ; and, fur- 
thermore, that each particular kind of fermenta- 
tion has its own peculiar microbe as the cause. 
This was an example of what we term to-day mi- 
crobic specificity, in marked contrast to views 
Microbic w ^^ cn were ^ nen prevalent regarding the variabil- 

specificity. ity of micro-organisms.* Pasteur then applied 

* "The following citation from Nageli illustrates clearly 
this idea of unlimited variability of microbes : 'In the 
course of generations the same species assumes alt-ernat 
ingly different morphological and physiological forms which, 
as years and periods of years pass by, may cause now 



VACCINATION. 5 

what he had learned about fermentations to the 
study of the diseases of wines and beers. He found 
their causes, and devised a preventive measure, 
which consisted merely in the destruction of the 
germs by heating the wine to a suitable tempera- 
ture before it was stored. At the instance of the 
French government, he then studied certain dis- 
eases of silkworms. His success in discovering 
their causes and prevention must always remain for 
us one of the landmarks of the world's progress. 
It was during the latter investigations that he 
took up the study of anthrax. The specific mi- 
crobe having been discovered, and the methods of 
transmission of the malady having been made 
clear through investigations by both Pasteur and 
Koch, Pasteur turned his attention to methods 
of prevention and, if possible, of cure. 

Pasteur pondered the question of smallpox vac- vaccina- 
cination. He came to believe that vaccinia is 
smallpox, the virus of which has been attenuated 
by its passage through the cow, and that conse- 
quently when man undergoes vaccination he there- 
by is inoculated with a benign form of the disease. 
Might not this be an example of a law which would 
be general in its application ? The protective inoc- 
ulation (active immunization) against the pleuro- 
pneumonia of cattle which had long been prac- 
ticed gave encouragement to this hope. Some 
work by Toussaint was important in the answer 
to this question. It was evident that a weakening 
or attenuation of the bacteria or virus must first 

souring of milk, now the formation of butyric acid in sauer- 
kraut, now the fermentation of wine, now the decomposition 
of albuminous matters, now the splitting up of urea, now 
tne red color of starchy food, and give rise now to diphtheria, 
now to typhoid fever, now to recurrent fever, now to 
cholera, now to malarial fever.' " (Cited from Hektoen, in 
Osier's System of Modern Medicine, Vol. I.) 



tioii. 



INFECTION AND IMMUNITY. 



Hydro- 



be obtained before it could be safely injected into 
animals for the purpose of producing immunity, 
for if the unaltered virus were injected the viru- 
lent infection would result. Accordingly, Tous- 
saint heated the blood of a sheep which had died 
of anthrax, to a temperature of 55° C. for ten 
minutes, then injected it into a number of sheep. 
Some of the animals died of anthrax, while others 
suffered only a mild attack from which they re- 
covered; the latter were found to be immune to 
a subsequent inoculation with virulent blood. In- 
asmuch, however, as some of Toussaint's animals 
had died of anthrax, Pasteur concluded that there 
was some grave error in technic. He considered 
that Toussaint's method probably killed or atten- 
uated the fully-developed bacilli, but did not in- 
jure the spores of the parasite (Koch had pre- 
viously shown the existence of anthrax spores). 
After much experimentation, Pasteur hit on the 
plan of growing the bacillus at a temperature of 
42° C, obtaining in this way a culture of the 
fully developed organism which had a low viru- 
lence, but which did not form the dangerous 
spores. When sheep were inoculated with the 
proper amount of this culture, which became 
known as anthrax vaccine, they had a mild attack 
of the disease, which rendered them immune to 
virulent inoculations. 

With the possibility of protective inoculation 
with a known virus actually demonstrated, sim- 
ilar procedures were tried with other animal dis- 
eases of known bacterial etiology, with the result 
that successful vaccines against chicken cholera 
and swine plague were developed. Somewhat 
later, having failed in their attempts to discover 



THEORIES OE IMMUNITY. 7 

the microbes of plague and cholera, Pasteur and 
his co-workers turned to the study of hydropho- 
bia. All efforts to cultivate the virus from the 
spinal cord of rabid dogs failed, although inocula- 
tion experiments proved its presence in this struc- 
ture. The unique idea then occurred to consider 
the infected spinal cord as a fully developed cul- 
ture of the virus. It remained to subject such a 
culture to the proper attenuating conditions for 
the purpose of weakening or actually destroying its 
virulence in order to make it fit for protective in- 
jections. This was accomplished by drying the 
cords in a closed vessel over a hygroscopic sub- 
stance (solid potassium hydroxid), the final viru- 
lence of the cord depending on the length of time 
it had been subjected to the drying process. The 
technic of the protective injections, the success of 
which is household knowledge, will be a subject for 
later consideration. 

Of primary importance, during this period, was T wo 
the work of Koch on the specific bacteria of tu- pS^eL 
berculosis, cholera, typhoid and the pyogenic dis- 
eases; and not least his improved methods of ob- 
taining pure cultures through the use of solid 
media (gelatin) on plates. Through his work and 
that of Pasteur two great principles had been 
set in motion ; the microbic specificity of infectious 
diseases, and protective inoculation in its general- 
ized form, through the use of attenuated virus. 

The scientific mind turned at once to the in- Theories of 
quiry, What changes in an animal body are re- of immunity. 
sponsible for the immunity which is acquired as 
the result of protective inoculations? Also, upon 
what properties of the tissues or body fluids does 
the natural immunity of an animal depend, and 



INFECTION AND IMMUNITY. 



Exhaustion 
Theory. 



Noxious 

Retention 

Theory. 



does the susceptibility of one species depend on 
the absence of those properties which characterize 
the natural immunity of another species? Pas- 
teur had observed that if he grew the microbe of 
chicken cholera in a liquid medium for some time, 
then removed the bacteria by filtration, the fluid 
became unfit for the further growth of the organ- 
ism on subsequent reinoculation. That is, the 
nutrient material had been used up; and he sug- 
gested that this is the case in the body of an ani- 
mal. Having undergone the infection, suitable 
nutrient material for the microbe is used up, and 
recovery ensues. The prolonged absence of the 
proper nutritious substances would account for 
the more or less permanent nature of the acquired 
immunity. This conception, the exhaustion 
theory, at one time shared by Koch and Klebs, is 
still represented in an altered form by Baumgar- 
ten, who speaks of an unfavorable culture medium 
as representing the condition of the immune body, 
which, of course, is broadly true. 

Chauveau was the author of another historic 
theory of acquired immunity (the noxious reten- 
tion theory), which maintained that during the 
course of a disease the bacteria produce substances 
in the presence of which they can not develop 
further; consequently recovery takes place, and 
the continued presence of these noxious substances 
renders another attack of the disease impossible. 
Although it is true that bacteria do not grow well 
in their own metabolic products, theories of im- 
munity on this and similar bases are not in ac- 
cord with the fact that immunity may be of great 
duration, and that it may be conferred by the 




PROPERTIES OF SERUMS. 9 

injection of the killed bacteria, or, in some cases, 
of their non-living soluble products. 

Metchnikoff may be .credited with having first »*»»soc^ 
offered a plausible explanation of natural resist- 
ance, founded on observation. As a zoologist he 
had studied the subject of intracellular digestion 
in the lower animals, and it was while working on 
this problem that he observed the fate of a yeast 
fungus (Monospora) , which caused epidemics 
among the daphnia, small, transparent animals 
with which he was working. Near the alimentary 
tract, which was the infection atrium, some large 
mesoblastic cells, which are perhaps analogous to 
the white blood cells, were seen to ingest the para- 
sites and dissolve them. If this took place to a 
sufficient extent the animals recovered; if, how- 
ever, the infecting organisms were too numerous 
or the reaction on the part of the animal insuffi- 
cient, the body became overwhelmed with para- 
sites and death resulted. Since that time Metch- 
nikoff has evolved his well-known theory of pha- 
gocytosis as the essential factor in both natural 
and acquired immunity, a theory which Pasteur, 
in his later years, looked on with favor. We may 
speak of this as the cellular theory of immunity; 
a theory which has had to undergo important 
modications in order to bring it into accord with 
new facts. 

Considering that natural or acquired immunity Inves tisa- 
must exist because of certain qualities of the body p^erties* 
cells, or of the body fluids, or possibly of both, of serums. 
investigators began to make analyses of the tis- 
sues; and of all the analyses, that which we may 
term the biologic has been the most fruitful. In 
this case biologic analysis means the detection of 



dal Power. 



10 INFECTION AND IMMUNITY. 

reactions which may occur when bacteria or their 
products are placed in contact with tissue cells 
or fluids, either in the living animal or in test- 
glass experiments. The chief of these are the de- 
Bacterici- termination of the ability of the serum of an ani- 
aal to kill bacteria or to neutralize bacterial 
toxins. These important investigations were in- 
augurated by the findings of Fodor, Nuttall, Nis- 
sen, v. Behring and Buchner, which showed 
that fresh defibrinated blood, and the blood 
serum of various animals, are able to kill bac- 
teria in the reagent glass. In contrast to the 
action of ordinary antiseptics, this power is 
often selective, killing one variety of bacterium 
and leaving another unharmed. This was of enor- 
mous importance, as it seemed to identify the 
factor on which natural antibacterial immunity 
depends. Then followed the discovery of Nissen 
and v. Behring (Vibrio metclinikovi) , and of 
Bouchard (B. pijoctjaneus) , that if an animal is 
systematically injected, i. e., immunized, with a 
micro-organism, the power of its serum to kill 
the bacterium used in the immunization is greatly 
increased ; from which it would seem that acquired 
immunity depends on the increase of powers which 
are normally present to a certain degree. These 
observations have to do with the bactericidal power 
of serum. 
Toxins ami Further progress was made through the discov- 
eries that the tetanus bacillus (Brieger and Fran- 
kel) and the diphtheria bacillus (Roux and Yer- 
sin) secrete each a powerful, specific, soluble toxin, 
which may be separated from the bacteria by fil- 
tration. Immunization with these bacterium-free 
toxins was undertaken (Behring and Kitasato, 



Antitoxins. 



TOXINS AND ANTITOXINS. 11 

1890) with the familiar result of the production 
of the specific antitoxins. Other investigations in 
this direction soon showed the independence of 
the antibacterial and the antitoxic properties of 
serums. 

With these facts in hand, the vigor with which 
investigations have been pushed may be readily 
imagined. The hope naturally prevailed that phy- 
sicians might become the masters of all infectious 
diseases, through the possession of specific anti- 
bacterial and antitoxic serums. But failures, with 
which we are only too familiar, met the attempts 
to produce adequate antiserums for many diseases. 
Nevertheless these failures, through stimulation 
to closer study, have resulted in the accumulation 
of much additional knowledge concerning the 
pathogenic properties of different bacteria, the 
nature of the immune serums and the various pro- 
tective factors of the body. Ehrlich has evolved 
a new theory of immunity from facts which were 
discovered in his laboratory, the "side-chain" 
theory, which it is the purpose to utilize in the 
interpretation of many reactions which will come 
up for consideration. 

Wright in England, Neufeld in Germany, and 
Hektoen in America more recently have led in a 
revival of interest in phagocytosis as a factor in 
natural and acquired immunity, with the result 
that there can no longer exist any doubt that pha- 
gocytosis plays an important role in protection 
against and in recovery from many infections. 
Thus the opsonins of Wright, and the bacterio- 
tropic substances of Neufeld, have served to bridge 
any chasm — never a real chasm — which seemed to 
exist between the so-called humoral and cellular 



12 INFECTION AND IMMUNITY. 

theories of immunity. The study of opsonins has 
also served to renew interest in a much-neglected 
field of specific prevention, namely, bacterial vac- 
cination, one of the most gratifying results of 
which has been a return to the tuberculin therapy 
of Koch. 

However, with all our resourcefulness, it is pos- 
sible that our limitations may soon be reached re- 
garding the serum and vaccinal therapy of many 
infections, and we shall be forced to try other prin- 
ciples of prevention and cure. In connection with 
this point, the newer chemotherapy, which has 
been developed in so brilliant a manner by Ehr- 
lich and others in relation to trypanosomiasis, is 
of the highest interest. It may be hoped that this 
work represents only the beginning of a new direc- 
tion of research, which will be of ultimate value in 
various bacterial as well as protozoan infections. 



PART ONE 

PRINCIPLES OF INFECTION. 



CHAPTEE I. 



Disease. 



PARASITISM, INFECTIOUSNESS, CONTAGIOUSNESS. 

Parasitism is the condition in which a plant, or parasitism. 
an animal being, lives on or within another living 
organism. A true parasite always derives its sus- 
tenance from the tissues of its host. 

An infectious disease is one which is caused by infectious 
living organisms which in some way have entered 
the body, where they multiply and liberate poison- 
ous substances. Accordingly the word has refer- 
ence to the nature of the cause of the disease. It 
is from the Latin injicere, meaning to place in or 
into. 

Some parasites may live on a host without 
causing appreciable damage; they are non-patho- 
genic parasites. In this case they may derive 
their nutrition from some of the excreted non-liv- 
ing products of the host, living as pure sapro- 
phytes, 1 or the amount of nutritious substance 
which they obtain from the host may be so little 
that the health of the latter is not impaired. This 
is true of organisms which normally inhabit the 
intestinal tract. 

1. A saprophyte is defined as a vegetable organism 
which lives on dead organic matter. An organism which is 
habitually saprophytic may become pathogenic under the 
proper conditions (bacillus of malignant edema). And, on 
the other hand, a pathogenic parasite lives a saprophytic 
life, when it grows in our artificial culture media. 



INFECTION AXD IMMUNITY. 



Infestation 
and Infec- 
tion. 



Bacteria and 
Protozoa. 



There is another large class of parasites, how- 
ever, which under proper conditions cause severe 
diseases in the host. Many pathogenic microbes live 
in and on the skin and mucous membranes with- 
out doing harm, but if certain ones reach the 
deeper tissues, they may institute pathologic proc- ■ 
esses (e. g., staphylococci, streptococci, pneumococ- 
ci, diphtheria bacilli and meningococci). Any or- 
ganism which is able to cause pathologic tissue 
changes, to disturb functions, and to set up ab- 
normal symptoms is classed as a pathogenic para- 
site. The abnormal processes which they institute 
are our infectious diseases. 

Where certain comparatively large organisms 
(macroparasites) exist on a body surface, as the 
skin or intestinal tract, the surface is said to be 
infested; the skin, for example, is infested with 
pediculi. One may also say that the intestinal 
tract is infested with tapeworms, but here the dis- 
tinction between infestation and infection is not to 
be drawn so sharply; surely when the larvae pene- 
trate the intestinal wall and reach the circulation 
or distant organs we must speak of infection. But 
even the adult tenia as it exists in the intestines 
may cause erosions of the mucous membrane or 
may perhaps burrow a slight distance into the 
wall, a condition which approximates the action of 
the larvae in passing through the wall; accordingly 
at some point the distinction between infestation 
and infection becomes an arbitrary one. 

The known pathogenic micro-organisms are 
grouped among the fungi, the bacteria and the pro- 
tozoa. Both the bacteria and fungi are vegetable 
in nature, complexity in form and methods of 
growth characterizing the latter, whereas the life 



BACTERIA AXD PROTOZOA. 15 

history of the former is simpler, and they multi- 
ply only by fission (fission fungi). Forms occur 
which appear to be intermediate between the true 
fungi and the true bacteria. The protozoa, the 
lowest forms of animal life, vary greatly in form 
and in the complexity of their life cycles. The 
highest protozoa, lead an intricate existence in 
which sexuality and alternation of hosts are some- 
times conspicuous features, as in the case of the 
parasites of malarial fevers, and possibly in that of 
yellow fever. In some instances the alternation 
of hosts is purely a facultative property, and not a 
necessity for the perpetuation of the species, al- 
though it is part of the natural cycle; this is the 
case with some of the trypanosomes, which can be 
transferred from animal to animal artificially for 
an indefinite period. 

There are certain infections, the causes of which 
are not known, and in some instances the organ- 
isms are considered as ultramicroscopic because 
they pass through bacteriologic filters. Theoretic- 
ally they may be either bacteria or protozoa. 

The known pathogenic micro-organisms may Types of mi- 
also be placed in one of the following three groups : 
1. Obligate parasites, which* are capable of growth 
only in a living organism (the bacillus of leprosy 
and the organisms of malaria). 2. Facultative 
saprophytes, which usually exist as parasites but 
may multiply on inanimate material under proper 
conditions. This group includes most of the path- 
ogenic microparasites. 3. Facultative parasites, 
which are saprophytic organisms living readily on 
inanimate material, but which may produce dis- 
ease when they reach suitable tissues in a host 



cro-parasites. 



isms. 



16 INFECTION AND IMMUNITY. 

(Bacillus teiani, bacillus of malignant edema, 
Amoeba dy sentence) . 
origin ana It is futile to speculate on the ultimate origin of 

Variations . . . . ° 

in organ- our various micro-organisms. It is sufficient to 
appreciate that the principles of biology and evolu- 
tion are broad enough to permit us to assume that 
some of the species which we now recognize may 
have arisen through the influences of environment 
and selection from other more or less closely re- 
lated species. However, investigations have shown 
that the essential characters of bacterial species are 
fixed more or less firmly,- suggesting that new spe- 
cies are likely to be developed only through a long 
course of time, or, if more quickly, through rare 
chance variations. Koch has suggested that among 
the trypanosomes found in different diseases some 
may still be too young in their differentiation to 
represent fixed species, although this cannot apply 
to the whole group of trypanosomes. 

Many micro-organisms do, indeed, show a great 
deal of flexibility in their physiology and viru- 
lence, with the result that they may approximate 
species which are usually recognized as being dis- 
tinct. Thus a strain of the diphtheria bacillus 
which loses its virulence is similar to a pseudo- 
diphtheria bacillus, and the cholera vibrio which 
has become a virulent resembles a number of other 
vibrios. The plague bacillus, whereas it commonly 
causes acute death in rats, may undergo such a 
change in the character of its virulence that it 
causes a chronic nodular inflammation. Some 
strains of the tetanus bacillus, which is habitually 
anaerobic, acquire the power of growing in the 
presence of atmospheric oxygen. By suitable 
passage a species of the tubercle bacillus may be 



VARIETIES OF ORGANISMS. 17 

made to resemble very closely in its cultural as- 
pects another species of this organism. On the 
whole, these are not large variations, and identifi- 
cation can be accomplished by one or more of the 
biologic reactions, such as the agglutination, bac- 
teriolytic or opsonic tests. 

In some instances the conditions are such that varieties. 
different species appear to represent only differ- 
ent grades or types of virulence of the same or- 
ganism. Those acid-fast bacilli which resemble 
the bacillus of tuberculosis form the most striking 
example of this. Bacilli of this character are com- 
monly found in various grasses or clover, which 
are used as food by cattle. Such organisms have 
a low grade of virulence, and when injected into 
animals cause the formation of only a nodule of 
granulation tissue, sometimes with the presence 
of giant cells, and the process heals readily. It is 
possible that certain of these organisms of more 
than usual virulence, or which may have acquired 
such virulence by residence in the alimentary tract 
of the ox, have retained their new pathogenic 
power as a permanent character, and that bovine 
tuberculosis originated in this way. It would be 
none the less logical to assume that the bacillus 
of human tuberculosis was derived from the bo- 
vine type in a similar manner. This can only be 
a subject for speculation, however. 

Bacteriologists frequently are able to place a 
number of species in a "group," the members of 
which resemble each other more or less closely, as 
the colon group, or the dysentery group. The 
members of a group may vary widely in their 
pathogenic power, whereas in other instances they 
produce similar diseases. Thus, Novy has shown 



18 INFECTION AND IMMUNITY. 

that, although the spirilla which cause the various 
relapsing fevers are very similar, they can be dif- 
ferentiated by means of immunity reactions, such 
as the agglutinating or protective powers of im- 
mune serums. 

A more detailed discussion of this aspect of 
general bacteriology would carry us too far afield. 
"infectious" Confusion sometimes arises concerning the sig- 
tasions." nificance of the words infectious and contagious 
and other words having similar roots. This con- 
fusion is due in large part to the fact that they 
have grown into a usage varying somewhat from 
that which originally adhered to them, and the 
dictionaries, even those which are medical in char- 
acter, have hardly kept pace with the transition. 

The significance of infectious is indicated in the 
definition of an infectious disease as given above. 
The word contagious, on the other hand, relates 
to a method by which some of the infectious dis- 
eases are transmitted from an infected person or 
animal to the healthy, namely, contact, direct or 
indirect. Not all infections are transmitted by 
contact, however, hence we may divide them into 
those which are contagious and those which are 
not. Communicable is often used as synonymous 
with contagious. 

Contagiousness is all the more striking in the 
case of acute infections which develop rapidly and 
soon after exposure. On the other hand, it is not 
so striking in a disease such as pulmonary tuber- 
culosis, which develops slowly and perhaps only 
after repeated exposures. 

The following rather general arrangement of 
the infectious diseases into groups according to 
the methods, and at the same time facility, of 



DISSEMINATION OF ORGANISMS. 



transmission is given in order to illustrate the 
idea and limits of contagiousness. 

1. Those which are characterized by ready trans- Facility and 

J ? Means of 

mission through the air. The micro-organisms are Transmission. 
discharged into the air from the respiratory 
passages, or from the skin in desquamative infec- 
tions, and it is only necessary for a susceptible 
person to come within the zone of infected air 
which surrounds the patient in order to acquire 
the disease. Actual contact with the patient may 
facilitate transmission in some instances, but is 
not necessan^ and many of them are transmitted 
by indirect contact, i. e., through the agency of 
intermediate persons, through food contamination 
(scarlet fever in milk), or through inanimate sub- 
stances which have been in contact with the pa- 
tient. These are all highly contagious "air-borne" 
diseases, which probably use the respiratory pas- 
sages as their infection atrium. Diphtheria, scar- 
let fever, measles, rotheln, smallpox, influenza, tu- 
berculosis, and plague in plague pneumonia are of 
this type. 

2. Transmission occurs almost exclusively by 
personal contact, and usually a special form of 
contact, never through the air: gonorrhea, syph- 
ilis, soft chancre, and perhaps dourine in horses. 
Syphilis occasionally is transmitted by indirect 
contact, the free period being a short one. These 
are contagious diseases. 

3. Transmission is chiefly by indirect contact, JoKac? 
or through food or water. Direct contact plays a 
role in some instances, and rarely the air may be 
a means of conveyance. The members of this 
group are not highly contagious in the sense of 
transmission directly from one individual to anoth- 



Personal 
Contact. 



INFECTION AND IMMUNITY. 



Not Trans- 
missible. 



Infectious 
Substances. 



er. The micro-organisms are excreted mainly by 
the feces, and typhoid and paratyphoid by the 
urine. As a rule they are acquired indirectly, as 
through a water supply or milk which have been 
infected from discharges, contamination of the 
hands from the excreta to food. Examples are ty- 
phoid, paratyphoid, cholera and dysentery. 

4. Transmission by means of insects. Some of 
these diseases, as malaria, yellow fever, and Eocky 
Mountain spotted fever, are not contagious at all, 
but are nevertheless communicable through the 
medium of the proper insect, mosquitoes or ticks. 
South African tick fever, ordinary relapsing fever, 
plague in some instances, trypanosomiasis, and 
probably typhus are other examples. The steps 
in transmission are sometimes very complex, and 
vary a great deal, as will be pointed out later. 

5. Transmission from man to man does not 
take place at all under ordinary conditions : tet- 
anus, hydrophobia, and other wound infections. 

It is thus seen that these five divisions consti- 
tute a series in which contagiousness finally disap- 
pears. The subject of transmission will receive 
further consideration later. 

It has been stated above that infectious diseases 
are caused by living pathogenic organisms. In- 
vestigations have shown, however, that the toxic 
products of some organisms can be prepared and 
separated from the organisms themselves by filtra- 
tion, and that such microbe-free toxins when in- 
jected into animals may cause the same symptoms 
that are produced by the bacteria themselves (teta- 
nus and diphtheria). Accordingly, for the sake of 
convenience, these toxins also may be considered 
among the infectious agents, even though sepa- 



CLASSIFICATION OF ORGANISMS. 21 

rated from their corresponding bacteria. The va- 
rious infections agents, including these toxins, find 
their proper places in the following classification, 
which, for the most part, is that of von Behring: 

I. Living (i. e., pathogenic parasites) . 

a. Macroparasites (e. g., intestinal worms, 

pediculi filarial, uncinaria). 

b. Microparasites. 

1. Bacteria (fission fungi: each cell di- 

vides into two in proliferating) . 

2. Fungi of more complex organization 

(e. g., aspergillus, oidia). 

3. Protozoa (e. g., Plasmodium mala- 

ria, Am aba coli). 

4. Filterable, ultramicroscopic or un- 
known micro-organisms. 

II. Non-living (i. e., toxins). 

a. Animal toxins (e. g., snake venom). 

b. Vegetable toxins. 

1. Non-bacterial (e. g., abrin, from the 

jequirity bean; ricin, from the cas- 
tor oil bean; the toxins of ha}' 
fever) . 

2. Bacterial. 

a. Soluble bacterial toxins (diph- 
theria and tetanus) . 

b. Intracellular bacterial toxins, 
which are not secreted by the 
cells in a soluble form. 

In the subjects to be considered we shall deal 
chiefly with microparasites and the diseases which 
thev cause. 



22 INFECTION AND IMMUNITY. 



CHAPTER II. 



Koch's Laws. 



INFECTIOUS ETIOLOGY. 

It is evident that the discovery of the specific 
organism of an infectious disease is of the great- 
est importance for purposes of serum therapy, vac- 
cination and hygienic prevention. For the demon- 
stration of a virus, it is not in all cases necessary, 
though desirable, that the organism be cultivated 
artificially, nor that it be recognized visually. The 
conditions in rinderpest may be cited in which the 
body fluids of a diseased animal, known to contain 
the infectious agent, are used for immunization, 
although the microbe itself can not as yet be culti- 
vated or recognized. 

There are so many possibilities of error, and so 
many errors have actually been made in regard to 
infectious etiology, that certain requirements in 
the way of proof are now habitually demanded be- 
fore a particular organism can be accepted as the 
cause of a disease. These requirements are most 
frequently expressed in the form of Koch's laws, 
which may be stated as follows 1. The suspected 
organism must be found constantly in the proper 
tissues of an animal suffering from the disease, or 
which has died from it. 2. The organism must be 
cultivated artificially in a pure state. 3. It must 
be possible to reproduce the disease in a suitable 
animal by inoculation with the pure culture. 4. 
The organism must again be cultivated in a pure 
state from the tissues of the experiment animal. 






KOCH'S LAWS. 23 

Since these laws were formulated another proce- Aseiutina- 
dure has been evolved which may give valuable 
evidence as to etiology. This pertains to the ag- 
glutination test, or, as we speak of it in connection 
with typhoid fever, the Gruber-Widal reaction. 
This principle, that in the acquiring of immunity 
to a microbic infection the serum of an individual 
gains in agglutinating power for the micro-organ- 
ism, has been found to hold true in many infec- 
tions. Consequently, if one has in hand the speci- 
fic micro-organism for a disease, he would expect 
the serum of a patient sick of this disease to have a 
stronger agglutinating power for this micro-or- 
ganism than for others which were accidentally 
present; and this power would also be greater than 
that possessed by the serum of one who had not 
had this particular disease. In spite of some pos- 
sibilities of error the agglutination test has been 
of distinct value in the recognition of the specific 
micro-organisms in certain diseases, as in the case 
of the germ of epidemic dysentery (Shiga). 

Also the more recent development of the opso- 
nins and, particularly, of the phenomenon of fixa- 
tion of complement, promise to be of value in the 
recognition of specific micro-organisms. 

All Koch's laws have not been complied with in obstacles 
certain cases, because of various difficulties Laws. ocl1 '* 
which have been encountered. First, the patho- 
genic protozoa can. not be cultivated on artificial 
media (we must except the success of Novy and 
McNeal with certain trypanosomes, and of Mus- 
grave and Clegg with the Amoeba coli under sym- 
biotic conditions) ; second, certain bacteria which 
may be found constantly in a given disease have 
not been cultivated artificially (spirillum of recur- 



24 INFECTION AND IMMUNITY. 

rent fever) ; third, there are a few diseases which 
are peculiar to man and accordingly can not be re- 
produced in experiment animals (leprosy, scarlet 
fever, measles, etc.) ; fourth, some infectious agents 
are pathogenic for experiment animals, but do not 
reproduce in them a clinical or anatomic condition 
identical with that found in the original animal 
(typhoid). 

Furthermore, failure to comply with all the re- 
quirements enumerated does not, in some cases, 
disqualify the organism as the causal factor. If 
an organism is found constantly in characteristic 
sites in a given disease and not in other infections, 
and if at the same time other microbes are not 
present or are present inconstantly or through ac- 
cident, there could be little or no hesitation in ac- 
cepting this organism as the cause of the disease, 
even if it were impossible to cultivate it or to trans- 
fer the disease to animals. The typhoid bacillus 
has been cultivated from characteristic foci (stools, 
blood, spleen, urine, rose spots) in such a large 
number of cases, and the bactericidal and agglu- 
tinating powers of the patient's serum against this 
organism are so distinctive, that compliance with 
the third law, though desirable, is not now essen- 
tial. The conditions are similar in reference to 
cholera and the cholera vibrio. 

The conditions are so unique in some diseases 
that, although all Koch's laws have not been met 
literally, certain equivalents have been met. To 
illustrate, we may consider an anopheles mosquito 
which has become infected with the plasmodium 
of malaria by biting a malarial patient, as a cul- 
ture medium ; and the transferring of the infection 



1XFECTJ0US DISEASES. 



to another patient by the bite of this mosquito as 
the inoculation experiment which is desired. 

The term "specific infectious disease" has come specific 
to have a very special meaning. It is applied to a Diseases. 
disease having characteristic clinical and anatomic 
phenomena, which can be caused only by one par- 
ticular micro-organism. Among the diseases 
which come within the limits of this brief defini- 
tion, the following may be enumerated (the micro- 
organism which is the cause of each disease being 
also given), for the sake of illustration. 



Diphtheria 

Tetanus 

Typhoid fever 

Cholera 

Anthrax 

Tuberculosis 

Leprosy 

Plague 

Dysentery (bacillary) 

Influenza 

Glanders (farcy) 

Chancroid 

Recurrent fever 
Gonorrhea 

Epidemic cerebrospi- 
nal meningitis 

Actinomycosis 

Blastomycosis 
Malaria 

Syphilis 



Bacillus diphtheria 
Bacillus tetani 
Bacillus typhosus 
Vibrio cholera 
Bacillus anthracis 
Bacillus tuberculosis 
Bacillus lepra 
Bacillus pestis 
Bacillus dysenteric 
Bacillus influenzae 
Bacillus mallei 
Bacillus chancri mollis 

(Ducrey) 
Spirillum obermeieri 
Micrococcus gonorrhoea 
Diplococcus intracellula- 

ris meningitidis (of 

Weichselbaum) 
Actinomyces bovis et 

hominis 
Blast omycetes and Oidia 
Plasmodium malaria? 
Spirochata pallida 



IXFECTIOX AXD IMMUNITY. 



Unknown 
Etiolog-y 



Obstacles to 

Discovery of 

Microbes. 



A large number of animal diseases have their 
specific microbes, as do certain other human dis- 
eases which hardly concern us as to the subject in 
hand. 

In addition to the diseases mentioned, there are 
several, of unknown etiology, which from analogy 
we must recognize as entities because of their con- 
stant clinical and anatomical manifestations. Scar- 
let fever, measles, German measles, chickenpox, 
smallpox, yellow fever, typhus fever and hydro- 
phobia, are undoubtedly due to micro-organisms. 
Mallory recently found in the skin of four scar- 
let fever patients a protozoon-like body which he 
believes to be the cause of the disease, although 
he admits that much desired proof has not been ob- 
tained. 

It is possible that smallpox and vaccinia will be 
eliminated from the diseases of unknown causa- 
tion, owing to the evidence of protozoon etiology 
that Councilman and his colaborers have obtained ; 
however, for the present, the question is sub judice 
in view of the fact that the forms described bear a 
close resemblance to certain well-known types of 
cell degeneration. 

The following animal diseases, of unknown 
etiology, may also be mentioned in this connec- 
tion: Foot and mouth disease, peripneumonia, 
bovine pest, sheep-pox (clavelee), chicken-typhus 
or chicken-pest and epithelioma contagiosum of 
fowls. 

The following appear to be the chief reasons for 
the failure to discover the organisms of these dis- 
eases : 1. Inability to cultivate the microbe. 2. 
Mixed, or symbiotic infections. For a long time it 
was supposed that the so-called hog-cholera bacillus 



SPECIFICITY OF ORGANISMS. 27 

is the cause of hog cholera. Eecent experiments, 
however, have disclosed that the true virus is ultra- 
microscopic and filterable, the bacillus being only 
a more or less constant associate. It is conceivable 
that in some cases the combined action of two 
micro-organisms may be necessary to cause the 
disease. The non-toxic products of the two may 
synthesize to form a toxic substance (Hektoen.) 3. 
Un stain ability of the microbe. 4. Ultramicro- 
scopic size. The organism of the peripneumonia of 
cattle was cultivated by Nocard and Eoux by grow- 
ing it in a closed collodion sac which was placed in 
the peritoneal cavity of suitable animals. It is so 
small that its form can not be made out, and 
growth is recognized only by clouding of the 
culture medium, and the increased virulence of the 
latter for animals. 

Some valuable information has been obtained FiiteraMiity 
by observing whether the infectious agents are 
so small that they will pass through dense filters 
of porcelain or infusorial earth. It has been- found 
that the viruses of foot and mouth disease, peri- 
pneumonia, rinderpest, sheep-pox, chicken-typhus, 
horse sickness, epithelioma contagiosum of fowls, 
yellow fever, hydrophobia, and hog cholera are fil- 
terable. This is determined by injecting the fil- 
tered culture medium, or serum into susceptible 
animals. The viruses of smallpox, vaccinia, and 
Eocky Mountain spotted fever are not filterable. 
Inasmuch as scarlet fever, measles, chicken-pox 
and typhus fever cannot be produced in animals, 
the filterability of their viruses is not at present 
susceptible to determination. 

There is a marked tendency in many diseases, 
typhoid, cholera, malaria, etc., for characteristic 



28 INFECTION AND IMMUNITY. 

organs or groups of organs to be involved in some 
particular manner. These are features which, 
together with a constant bacteriology, stamp them 
as specific diseases. On the other hand, a large 
number of micro-organisms cause no well-defined 
clinical and anatomic disease, but, depending on 
various accidents, cause an inflammation now in 
one organ, now in another. 

Eegarding the production of suppuration, the 
pyogenic power is common to a large number 
of microbes. A diphtheritic or pseudo-diphtheri- 
tic process in the mouth and throat may be caused 
by the diphtheria bacillus, streptococcus, staphylo- 
coccus, oidium or yeasts ; bronchitis may be caused 
by the influenza, tubercle, plague and typhoid 
bacilli, and by the infecting agents of the acute 
exanthemata, etc. ; pulmonitis by the pneumococ- 
cus, streptococcus, tubercle, plague, Friedlander 
and influenza bacilli, oidium, actinomyces, etc. ; 
meningitis by the tubercle and influenza bacilli, 
streptococcus, staphylococcus, pneumococcus, gono- 
coccus, diplococcus of epidemic meningitis, the 
syphilis virus, etc.; arthritis by the streptococcus, 
staphylococcus, tubercle bacillus, gonococcus, the 
virus of rheumatic fever, etc. ; endocarditis by the 
streptococcus, staphylococcus, gonococcus, pneu- 
mococcus, tubercle bacillus, etc., and septicemia 
by a whole host of organisms aside from those 
mentioned as causing specific diseases. 

Within certain limits, however, there is often a 
degree of specificity in the processes produced by 
some of the organisms mentioned, which some- 
times allows of clinical and anatomic differentia- 
tion. The infiltrating and rapidly extending in- 



SYMBIOSIS. 29 

vasion of the subcutaneous and connective tissues 
caused by the streptococcus can often be distin- 
guished clinically from the slower, more circum- 
scribed process caused by the staphylococcus. The 
conditions induced by the Bacillus aerogenes cap- 
sulatus, the bacillus of malignant edema, are, in 
turn, different from those of the streptococcus and 
staphylococcus. The pneumococcus commonly 
causes the consolidation of rather extensive areas 
of the lung, whereas the streptococcus and the 
bacillus of Friedlander are more often found in 
the lobular consolidations. The membranous in- 
flammation of diphtheria may in favorable cases 
be distinguished from that of the pyogenic organ- 
isms without bacteriologic aids ; in this possibility, 
however, there lies no justification for neglect of 
the bacteriologic examination. 

In nature pathogenic micro-organisms are often 
found side by side with saprophytes or with other 
pathogenic bacteria, and at times their viability is 
profoundly influenced by their associates. Thus 
it is found that the bacilli of plague and typhoid 
and the vibrio of cholera do not live long in the 
presence of many saprophitic organisms. In some 
instances this may be due to the exhaustion of the 
nutrient material by the more rapidly growing 
saprophytes, whereas in others it may be referable 
to an antagonistic action of one organism on the 
other. On the other hand, the relationship may be 
a favorable one. The existence of anaerobic or- 
ganisms in nature, such as the tetanus bacillus or 
the bacillus of malignant edema, may be favored 
by a luxuriant growth of aerobic organisms in 
their immediate vicinity. 



30 INFECTION AND IMMUNITY. 

This relationship is investigated experimentally 
either by growing two organisms in mixed cul- 
tures, noting subsequently whether one has out- 
grown the other/ or one may be grown on a me- 
dium which has previously been utilized by the 
other. The predominance of one or the other may 
depend on the nature of the culture medium. This 
principle is utilized in obtaining pure cultures of 
the cholera vibrio from dejecta by the use of a 
strong alkaline medium which favors the growth 
of the cholera vibrio but inhibits that of the other 
intestinal bacteria. Similarly the diphtheria bacil- 
lus grows well on Loeffler's blood serum, whereas 
the other organisms commonly found in the throat 
do not. 

Garre distinguished a one-sided and a mutual 
antagonism between bacteria, but the former seems 
to be the more common. Examples of favorable 
symbiosis on suitable culture media are the fol 
lowing : Streptococcus and cholera vibrio ; anthrax 
and pyocyaneus bacilli (Turro) ; diphtheria bacil- 
lus and the streptococcus (Hilbert). In plate cul- 
tures it has been found that the influenza bacillus 
produces unusually large colonies when they lie 
adjacent to colonies of the staphylococcus (Grass- 
berger), and that it grows vigorously on agar 
which contains killed bodies of the gonococcus or 
diphtheria bacillus (Cantani). It has been noted 
that the diphtheria bacillus is stimulated to a 
greater production of toxin by the presence of 
streptococci. 
Mixed The coexistence of two or more micro-organisms 
in a morbid condition is of frequent occurrence, 
and some of the most interesting and important 



Infections 



MIXED IXFECTIOXS. 31 

phenomena of infectious diseases are referable to 
mixed, secondary or superimposed infections. 

Two exogenous infections may attack an indi- 
vidual at the same time. Measles and scarlet fever 
and diphtheria and scarlet fever have been known 
to coexist. Pneumococcus pneumonia and typhoid 
fever, chancre and soft chancre with pus cocci, 
syphilis and gonorrhea, diphtheria with strepto- 
cocci, tetanus with gangrene-producing organisms, 
are common observations. One organism may in- 
tensify the virulence of another. Diphtheria ac- 
companied by streptococcus infection seems to be 
more virulent than diphtheria alone. It is also 
believed that the presence of aerobic organisms 
(those which demand oxygen for their develop- 
ment) in a wound infected with the tetanus bacil- 
lus or the bacillus of malignant edema (anaerobic 
organisms), may increase the virulence of these 
infections. Streptococci are probably important 
organisms in scarlet fever, for they are present in 
unusual numbers in the throat lesions and are 
often found in fatal cases in all the organs, yet it 
is possible that they inaugurate only a mixed or 
secondary infection superimposed on that of the 
scarlatina virus. The conditions are somewhat 
similar in smallpox, the pustules of which invari- 
ably contain streptococci, staphylococci, or both. 
In both scarlatina and smallpox these secondary 
infections may be responsible for many fatalities. 

Pneumococcus pneumonia occurring during the 
course of, or during convalescence from the erup- 
tive fevers, diphtheria, typhoid fever or erysipelas ; 
a streptococcus septicemia developing during 
typhoid (giving rise to an irregular temperature 



32 INFECTION AND IMMUNITY. 

curve), streptococcus infection of tubercular cavi- 
ties, and the development of acute tuberculosis 
during measles — these are important examples of 
secondary infections. 

We should naturally expect that the presence of 
a severe secondary infection might embarrass at- 
tempts at serum therapy and vaccinal therapy. 
Experience regarding the former is limited prac- 
tically to diphtheria, and there is no lack of evi- 
dence to show that the disease when complicated 
by severe streptococcus infection sometimes can- 
not be controlled by antitoxin treatment; and in 
vaccinal therapy (injection of micro-organisms or 
their products) it is emphasized from all sides that 
in the presence of mixed infection it is advisable 
to inject preparations of the secondary as well as 
the primary organisms concerned. 



CHAPTER III. 



INFECTION ATRIA AND THE EXCRETION OF MICRO- 
ORGANISMS. 

Infection Atria. 

The infection atrium is the primary point of 
invasion by micro-organisms, or the point or tissue 
or surface through which they reach internal 
structures. 

In general, micro-organisms may enter the body 
through any of its surfaces, except, of course, the . 
serous coverings. Anatomical structure, however, 
renders the skin, and other surfaces which are 
clothed with pavement epithelium, quite resistant 
to penetration, in the absence of wounds. Leav- 
ing wound infection out of consideration the mu- 
cous surfaces afford the most frequent points of 
entrance. 

Certain micro-organisms appear to have a predi- p re ferre 
lection for particular tissues, preferring one point aSX? 
of entrance or primary involvement above all 
others. Thus, in so far as we know, the typhoid 
bacillus and the cholera vibrio always produce 
their primary infection in the intestines, although 
a hematogenous typhoid is sometimes spoken of, 
the true atrium escaping detection. The diph- 
theria bacillus habitually makes its attack in the 
upper respiratory passages. It is probable that 
measles and scarlet fever utilize the respiratory 
tract for the point of invasion, although this can- 
not be determined positively at present. As will 
be described later, many microbes have a predilec- 



34 INFECTION AND IMMUNITY. 

tion for certain tissues after they reach the interior 
of the body. 

Sometimes it would appear that a particular 
surface is predilected only because it is the area 
which is most commonly exposed to infection. 
Thus, syphilis is usually a venereal disease, al- 
though on proper exposure chancres occur readily 
on the lip, the mucous membranes of the mouth, 
tonsils, or through wounds in the skin. Hence 
the predilection of the primary sore for the geni- 
tals is only apparent. Also the diphtheria bacillus 
occasionally is inoculated into wounds on cutane- 
ous surfaces and in the vagina. Some mucous 
surfaces are protected against microbic invasion 
by the character of their secretions, as in the cases 
of the stomach and vagina (See under "Natural 
Immunity"). 
cryptogen- In the so-called cryptogenetic infections the 
etlc Viotis" atrium escapes detection. Certain micro-organisms 
may enter the body without causing a discoverable 
reaction at the point of entrance (plague). Ex- 
perimentally it has been shown that tubercle ba- 
cilli readily pass through the intestinal wall into 
the mesenteric lymph glands without causing le- 
sions of the intestines. Leucocytes may carry or- 
ganisms through the intact surface of the intes- 
tines into the deeper tissues, and possibly the same 
process occurs in the lungs, particularly in rela- 
tion to the tubercle bacillus ( !). 
ski it. Infection through the skin commonly take? 
place through wounds (tetanus, glanders, malig- 
nant edema and purulent infections), although the 
wound may be so small as not to be discoverable 
(bubonic plague). "Insect-borne" diseases are 
inoculated through the skin by the bites of the 



1XFECTI0N ATRIA. 



insects. In the case of plague the bacilli may be 
deposited on the skin in the feces of the flea and 
subsequently inoculated by means of rubbing or 
scratching. The guinea-pig may be infected with 
plague by rubbing a culture on the shaven skin. 
Minute wounds probably exist. Staphylococci may 
reach the hair follicles as a consequence of rub- 
bing and cause furunculosis after penetrating the 
soft epithelium of the follicle. 

The conjunctiva has rather high resistance for 
some micro-organisms, as the anthrax bacillus, 
and it harbors staphylococci continuously. It may 
be invaded, however, by the gonococcus (especially 
in children), pneumococcus, streptococcus, staphy- 
lococcus, diphtheria bacillus, Morax-Axenfeld ba- 
cillus, and probably the meningococcus. The 
plague bacillus will cause generalized infection 
through the conjunctiva in rats, and it is reported 
that glanders and hydrophobia (Conte, Galtier) 
may also gain entrance through the conjunctiva. 

The nasal passages become infected with the 
organisms causing coryza, with the organisms of 
diphtheria, influenza, glanders, leprosy and with 
the pyogenic cocci. Some of these may extend to 
the adjacent cavities, antrum of Highmore, frontal 
sinuses, and the middle ear through the Eustachian 
tube. On account of the proximity of the nasal 
passages to the brain, and the lymphatic communi- 
cations, it is probable that meningitis (pneumo- 
coccic and epidemic cerebrospinal) often arises by 
extension of the organisms from the nose to the 
meninges through the ethmoid. 

Actinomycosis, syphilis, occasionally tuberculo- 
sis (tongue), noma, thrush, and in children gon- 
orrhea may find primary location in the mouth. 



Eye. 



Nasal 
Cavities.. 



36 



INFECTION AND IMMUNITY. 



Stomach 

and 

Intestines. 



Streptococci, pneumococci and diphtheria read- 
ily attack the tonsils, and it is probable that the 
tubercle bacillus often enters through them, with 
or without causing local infection. Similarly it is 
believed by many that organisms causing septice- 
mia (particularly the streptococcus), acute articu- 
lar rheumatism, and osteomyelitis may enter 
through the tonsils, and this may also be the case 
in scarlet fever. 

The bronchi become infected by the various or- 
ganisms causing bronchitis (streptococcus, pneu- 
mococcus, influenza bacillus, etc.), and, either 
through surface or lymphatic extension, or by deep 
inspiration, these and many other organisms, as 
the tubercle and plague bacilli, and the actino- 
myces, reach the deeper recesses. Some of the ex- 
anthemata, as measles and smallpox, may find en- 
trance through the pulmonary tissue. As explained 
later, "dust infection" and "droplet infection" are 
of great importance in pulmonary involvement, 
particularly in relation to tuberculosis. "Pri- 
mary" tuberculosis of the peribronchial lymph 
glands indicates that some micro-organisms may 
traverse the bronchi without involving them. 

The stomach is comparatively free from infec- 
tions. The intestines provide an atrium for ty- 
phoid, cholera, dysentery (bacillary and amebic), 
tuberculosis, plague, anthrax, in children for the 
streptococcus, Bacillus pyocyaneus and others; in 
animals, for anthrax, plague, swine plague, mouse 
typhus, chicken cholera, hemorrhagic septicemias, 
intestinal diphtheria of rabbits, and others. 

The extent to which micro-organisms are carried 
from the intestines into the body in a state of 
health is greatly disputed, but frequent existence 



Tract. 



INFECTIVITY OF EXCRETIONS. 37 

of primary tuberculosis of the mesenteric lymph 
glands indicates that it probably occurs. 
Rectum. — Gonorrhea, septic infection of hemor- Rectum and 

, . , , x Genito- 

rllOldal Veins. TJrinary 

Urethra. — Gonorrhea, syphilis; "simple" ure- 
thritis due to other causes. 

Bladder and Ureters. — Infection usually second- 
ary, by extension or from the blood stream. 

External Genitals. — Hard and soft chancres. 
Diphtheria in girls. 

Female Genital Tract. — Gonorrhea, especially in 
the cervix, which is covered by soft cuboidal epithe- 
lium. The vagina is quite resistant owing to its 
covering of pavement epithelium and the bacteri- 
cidal character of its secretion. Virulent pyogenic 
organisms sometimes are found in the normal 
vagina and they may occasionally be responsible 
for puerperal infections. 

The above refers to primary invasion. It is well 
known that many of these surfaces and the organs 
which they cover are frequently involved subse- 
quent to initial infection at some other point. This 
is secondary, or, better, metastatic infection. 

Excretion of Micro-organisms. 
In the transmission of an infection from person 
to person, without the intervention of an inter- 
mediate host (insects), the process naturally pre- 
supposes that the micro-organisms are excreted or 
discharged from the body of the patient through 
one channel or another. Regarding the likelihood 
of transmission, in the event of excretion, this 
will depend on the character of the organism, its 
viability under the conditions of excretion, the in- 
fection atrium which it demands, and whether or 



38 INFECTION AND IMMUNITY. 

not it is discharged in such manner that it is read- 
ily disseminated. Some of these points are con- 
sidered in following chapters. 
Relation of As a general principle it may be stated that 
Excretion ^o w ^ n ^ lg sivr f aces f the body are the seat of infec- 
luvoivement. ^ Qn ^ e micro-organisms are discharged into the 
outer world more or less easily. This applies not 
only to the cutaneous surface, but also to the mu- 
cous surfaces, as the lungs, alimentary tract, gall- 
bladder, and urinary bladder, and also to discharg- 
ing sinuses and abscesses which rupture through a 
cutaneous or mucous surface. The surfaces maj 
be involved either primarily, as in tuberculosis or 
blastomycosis of the skin, or as a part of a gener- 
alized infection, as in the case of some of the 
eruptive diseases. Thus from the respiratory pas- 
sages the microbes of pneumonia, tuberculosis, 
diphtheria, tonsillitis caused by other micro-organ- 
isms, plague pneumonia, influenza, whooping- 
cough, epidemic cerebrospinal meningitis and 
probably measles, scarlet fever and smallpox, are 
discharged into the surrounding air. From the 
intestinal tract the micro-organisms of tubercu- 
losis, typhoid fever, cholera and of other less im- 
portant diseases reach the outer world. From the 
genito-urinary tract, those of gonorrhea, syphilis, 
tuberculosis, typhoid and parat} r phoid fevers; from 
the skin the microbes of ulcerative processes, the 
contagious dermatoses, trichophytosis, favus, etc.. 
and probably some of the contagious exanthemata 
(scarlet fever, measles, etc.). 
Metastatic Of great importance is the fact that some infec- 

Infections. ,. -, • -. •-, , i 

tions which are primarily systemic, or become so 
during the course of infection, commonly involve 
some excreting organ secondarily, thus rendering 






INFECTION CARRIERS. 39 

possible, or increasing, the discharge of the organ- 
isms. In a large percentage of the cases of typhoid 
fever the kidneys become the seat of numerous 
foci of metastatic infection, resulting in the elim- 
ination of large quantities of living, virulent ty- 
phoid bacilli in the urine. A similar event happens 
in parat/yphoid fever, and in systemic tuberculosis, 
and Koch has even suggested that sleeping sickness 
may be acquired by coitus. "Milk sickness," which 
apparently is acquired through the gastrointes- 
tinal tract, is transmitted through the milk (Jor- 
dan and Harris), and the same is true of Malta 
fever. The virus of hydrophobia is excreted 
through the salivary glands. Experimentally, 
pneumococci and anthrax bacilli, when injected 
into the circulation, have been recovered from the 
intestinal tract. This was also done with the 
vibrio of cholera in guinea-pigs (Kolle and 
IssaefY). 

These statements are made with reference to 
the discharge of micro-organisms during actual 
disease. Investigations have shown, however, that 
infections on a large scale, reaching even epidemic 
proportions, are frequently derived from those who 
apparently are in a state of good health. Usually, 
but not always, this concerns individuals who have 
suffered from the infection at some previous time, 
and they are known as "bacillus carriers," or sim- 
ply "carriers." 

The vibrio of cholera may be excreted in the 
stools for forty-eight days after the recovery of 
the patient (Kolle). Virulent diphtheria bacilli 
may be discharged from the mouth and nose for 
months after recovery from the disease, and in the 
case of rhinitis fibrinosa chronica this may persist 



40 INFECTION AND IMMUNITY. 

for years. "Latent" gonorrhea is frequently in- 
fective. The urine after recovery from typhoid 
fever may contain the bacilli for months (Pe- 
truschky and others), and the recent study of ty- 
phoid carriers has shown that they may discharge 
bacilli in the stools for many years (twenty or 
more). In some instances it has been supposed 
that the gall-bladder is in a state of chronic in- 
fection with the bacilli and serves as a reservoir 
for continuous flooding of the intestines. The 
value of the remedial measure suggested — i. e.., the 
extirpation of the gall-bladder — has not yet been 
demonstrated. We cannot leave out of mind the 
possibility^ that the typhoid bacillus, in some in- 
stances, may become habituated to the intestinal 
environment and multiply there; in such cases it 
would not be necessary to assume another source 
of replenishment. The dissemination of* micro- 
organisms by insects which have fed on infected 
blood is apart from excretion and is considered 
under the subject of "Insect Transmission" Chap- . 
ter VI.). 




CHAPTER IV. 



SOURCES OF PATHOGENIC MICRO-ORGANISMS. 

(1) Earth, Etc.; (2) Food Substances; (3) Ani- 
mals; (Jf) Body Surfaces of the Individual. 

Micro-organisms which produce disease in man 
may be derived (1) from the earth, other inani- 
mate material, or from vegetable growth; (2) 
from water, milk or other food substances; (3) 
from animals, directly or indirectly; (4) from the 
body surfaces of the individual himself; (5) from 
other human beings, and (6) from insects. 

1. The extent to which the superficial earth is Eartn. 
contaminated with micro-organisms depends on 
various conditions, particularly the presence of 
dead organic matter, moisture, temperature, the 
degree of exposure to light and sunlight, the chem- 
ical composition of the soil, and the admixture of 
animal excretions. Some of them inhabit the soil 
naturally and are comparatively harmless sapro- 
phytes, and may even be of great value in the 
regeneration of soils. Others, of pathogenic char- 
acter, seem to occur naturally in the earth or on 
vegetation, where they multiply readily (the pyo- 
genic cocci, actinomyces). On the other hand, a 
large number of pathogenic organisms reach inan- 
imate nature only as they are deposited with the 
excretions of man (those of typhoid, paratyphoid, 
dysentery, cholera, plague, tuberculosis, etc.), or of 
animals (tetanus bacilli). Manjr, as the organisms 
of typhoid, cholera and plague, probably do not 
proliferate at all in the earth, although some (tet- 



42 INFECTION AND IMMUNITY. 

anus bacillus and that of malignant edema) re- 
tain life and virulence for a long time. It is still 
uncertain whether the latter proliferate in this sit- 
uation, or whether they persist merely through the 
agency of their resistant spores. Inasmuch as they 
are anaerobic in character, their life may in some 
instances be prolonged through symbiotic aerobic- 
organisms, which surround them and create for 
them an atmosphere which is poor in oxygen. The 
presence of many saprophytes is unfavorable to 
the life of certain micro-organisms in the soil (ty- 
phoid, plague). In so far as is known none of 
the protozoa which are pathogenic for man occur 
in the soil naturally. 
water, and 2. Water, milk and other food substances rarely 
?nbJtance* harbor important pathogenic organisms under nat- 
ural conditions. On the other hand, they play a 
very important part in carrying such microbes 
from man to man, and in some instances from 
animals to man, as explained in succeeding chap- 
ters. Stagnant water frequently sets up acute enter- 
itis, which may in some instances be due to its 
chemical constituents and in others to saprophytic 
organisms. 

Solid foods, as fruits and vegetables, may occa- 
sionally harbor bacteria, particularly when in a 
state of decay, which have moderate pathogenic 
powers for the intestinal tract; or, by providing 
suitable alimentation or otherwise modifying the 
contents or resistance of the alimentary tract, mav 
render organisms virulent which otherwise would 
be harmless. 

Meats, healthy in the first instance, are subject 
to invasions by micro-organisms from the intes- 
tinal tract, after the death of the animals (fowls, 



INFECTION FROM MILK. 43 

fish, oysters), or the}' ma}' be contaminated by 
unclean and improper preservation later. The 
symptoms caused by their ingestion are actual in- 
fections in some instances (as with Bacillus enter- 
itidis), whereas in others the condition may be one 
of intoxication by the products of saprophytic ac- 
tivity (Bacillus botulinus) . 

Some vegetables contain highly poisonous alka- 
loids and toxins, which rarely find a place in dis- 
ease. Some of them have been of great value in 
the experimental study of toxins and antitoxins. 
(See table at close of Chapter I.) 

3. Animals are sometimes subject to infection Animals. 
by microbes which are also pathogenic for man, 
transmission taking place through the consump- 
tion of diseased meat or milk, or through direct 
or indirect contact, through wounds, or by the 
bites of insects. 

In bovine tuberculosis the udder is frequently Milk. 
involved, and in such cases large quantities of the 
bacilli are excreted by the milk. Although the 
virulence of the bovine bacillus for man may not 
be so great as that of human tuberculosis, it is 
now well established that it often infects man, 
perhaps children more frequently than adults. The 
cow's udder is occasionally involved in infections 
with streptococci, which, being excreted in the 
milk, are capable of causing severe enteritis when 
the milk is ingested. 

The micro-organism of milk sickness is trans- 
ferred in a similar way, and only recently it has 
been shown clearly that man (in Malta) becomes 
infected with Malta fever by the consumption of 
the milk of goats. A very large percentage of these 



44 



INFECTION AND IMMUNITY. 



animals was found suffering from the disease, and, 
since the use of goat's milk has been prohibited, 
the incidence of the disease in man has undergone 
an astonishing decrease. It seems to have beeu 
demonstrated that both horses and cattle occa- 
sionally suffer from generalized infections with the 
paratyphoid bacillus, and with Bacillus enteritidis. 
and epidemic infections with the former have been 
traced to the consumption of diseased meats. Bot- 
ulism and trichiniasis are derived in the same 
way. In some instances infection of the meat 
probably takes place during or subsequent to 
slaughtering. 
By contact. Anthrax, glanders and actinomycosis are con- 
veyed to man from animals by contact, the first 
two being contagious ; and hydrophobia by the bites 
of rabid animals — i. e., by wound infection. 
By insects. In a few instances infections are transmitted 
from an animal to man by means of insects. Thus, 
the conveyance of plague from the rat by the flea 
is one of the means by which man contracts this 
disease. The tsetse fly of South Africa, which 
inoculates man with the trypanosome of sleeping 
sickness, seems to derive its infection from wild 
animals in some instances, although human pa- 
tients are also an important source of infection for 
fresh flies. The virus of Eocky Mountain spotted 
fever probably passes at least a part of its exist- 
ence in the body of one or more species of small 
wild animals, and this step seems necessary 
for the maintenance of virulence. In connection 
with malaria, relapsing fever, South African tick 
fever and the piroplasmoses a third host seems to 
play no role, or, at any rate, not a necessary role. 



Infection." 



AUTOINFECTION. 45 

Snake venoms, and the poisons of spiders, bees, 
and various insects, are toxins of animal origin 
which have pathologic and scientific importance. 

4. "Endogenous" infection or "autoinfection." "Auto. 
By this term we mean infection of an individual 
by micro-organisms which reside naturally on 
some surface of the body. Such organisms pro- 
duce infection only when some other factor, par- 
ticularly traumatism, comes into operation. 

Hair follicles frequently contain staphylococci 
and when occlusion occurs the organisms may pro- 
duce a pustule or a furuncle. An injury of the 
conjunctiva may result in infection by staphy- 
lococci or pneumococci, which are present normally, 
and many wound infections are due to organisms 
which pre-exist on the surface. 

Probably a factor of great importance for the 
invasion of such organisms is a condition of low- 
ered resistance on the part of the tissues. We 
know, for example, that virulent streptococci and 
pneumococci are frequently found in the pharynx 
and on the tonsils in apparent health. Exposure 
to cold in some instances may be the means of 
lowering the resistance of the surfaces (inhibition 
of the antibacterial forces) so that the organisms 
become more numerous and penetrate the sur- 
face. Observations suggest also that the presence 
of a serous exudate, such as exists even in a tran- 
sient inflammation, may cause an increase in the 
virulence of the organisms which are bathed by it. 
Similar forces may play a role in the bronchitis 
and pneumonia which follow exposure. 

There seems to be comparatively little danger of 
"autoinfection" from pathogenic bacteria which 
exist normally in the intestinal tract, except in 






46 INFECTION AND IMMUNITY. 

the case of traumatism, as in incarcerated hernia, 
or in severe constipation, or when the normal 
resistance of the intestines has been much dis- 
turbed by improper food. 

Sometimes an attack of a disease represents a 
recrudescence or reinfection by organisms which 
have persisted at some point following a previous 
attack. Eelapses of typhoid fever and recurrences 
of facial erysipelas, and frequently the flaring up 
of an old (latent) gonorrhea, illustrate this. Acute 
miliary tuberculosis, or tuberculous meningitis, 
may follow the escape of bacilli into the circulation 
from an unsuspected focus in a peribronchial 
lymph gland. This manifestly is not autoinfec- 
tion or endogenous infection, since, even in the 
old latent foci, the infection dates back to a prior 
invasion. 






CHAPTER V. 



Atriuni to 
3Ietliod of 
Excretion. 



SOURCES OF PATHOGENIC MICRO-ORGANISMS 

(Continued.) 
(5) From Man to Man. 

As indicated in Chapter I. there are all degrees 
in the facility with which infections diseases are 
transmitted from one person to another, varying 
from that in which it is only necessary to breathe 
the air surrounding a patient (scarlet fever, 
measles, influenza, etc.), to that in which trans- 
mission never takes place under ordinary circum- 
stances (tetanus, hydrophobia). 

In some instances a logical relationship exists Relation of 
between the facility of transmission, on the one 
hand, and the form of excretion of the micro-or- 
ganisms and their preferred infection atrium, on 
the other. Thus in many diseases in which the 
micro-organisms are excreted from the respiratory 
passages the latter are also used as the infection 
atrium (influenza, measles, smallpox, etc.). In 
others, in which they are excreted mainly by the 
intestines, the infection atrium is the intestines 
(typhoid, cholera, dysentery). Even if it were 
possible for the organisms of typhoid and cholera 
to gain entrance through the lungs (and indeed it 
may be possible in typhoid at least), the fact of 
their excretion mainly by the stools, and by the 
urine in typhoid, would render primary pulmonary 
involvement difficult. They reach the intestines 
more readily through contaminated food, water, 



Conveyance. 



48 INFECTION AND IMMUNITY. 

etc., than they could reach the lungs through in- 
fected dust or droplets. Similarly, if the virus of 
scarlet fever, which is excreted from the lungs and 
skin, could cause infection only through cutaneous 
wounds, rather than through the air passages, there 
is reason to believe it would not hold its pres- 
ent position as a very contagious disease. Among 
the communicable diseases we have to recognize 
that each has its own mechanism for habitual 
transmission, although the habitual mechanism 
may be departed from on many occasions. 
Mediums of As would be supposed, the diseases which are 
most readily acquired, the most contagious, and 
the most prevalent are those in which the micro- 
organisms are excreted into the air from the res- 
piratory passages, and in which also- the respira- 
tory passages are the preferred infection atrium. 
The medium of conveyance — i. e., the air — is used 
alike by all individuals. Some other diseases, much 
less contagious than those mentioned, may pre- 
vail in extensive epidemic form, often exceeding 
scarlet fever, measles, etc., in the percentage of 
incidence, as in the cases of cholera and typhoid 
fever. This is commonly due to an infected water 
supply, and the distribution of the disease cor- 
responds in large degree to that of the contami- 
nated water. In other words, the epidemic is co- 
extensive with the use of the conveying medium. 

Similarly, the prevalence of gonorrhea and syph- 
ilis depends' on the extent of promiscuous sexual 
intercourse; and, of malaria and yellow fever, on 
the number of individuals who become bitten by 
the infected Anopheles or Stegomyia mosquitoes. 

Thus the central factor in the communication 
of infection is suitable contact with the agency 



MEDIUMS OF CONVEYANCE. 



of conveyance, and where such contact can be re- 
alized with difficulty communication from person 
to person rarely occurs (e. g tetanus and hydropho- 
bia, in which wound inoculation is required). 

It is probable that the air, in the absence 
of atmospheric currents, would soon become ster- 
ile, by virtue of the effect of gravity in carrying 
the microbes to the earth, and the germicidal ac- 
tion of sunlight and diffuse light. Of course, these 
conditions do not prevail, or are not effective, and 
the air stands as one of the important agencies by 
which virulent micro-organisms reach the individ- 
ual, either from other individuals and animals or 
from inanimate nature. 

For a long time it was supposed that convey- 
ance through the air takes place chiefly or entirely 
through the medium of fine particles of dust which 
are laden with micro-organisms ("dust infection") . 
It was only through fundamental work by Flugge 
(1897) and others that it was shown how minute 
droplets of saliva or mucus from the lungs or nasal 
passages are fully as important as dust, and per- 
haps more important, for the transfer of infection 
from one individual to another. This is "droplet 
infection." 

The fields occupied by dust infection and drop- 
let infection do not coincide exactly. Only those 
diseases can be concerned in droplet infection in 
which infected droplets are discharged from the 
body — i. e., chiefly from the upper respiratory pas- 
sages. Since the infective droplets of saliva, 
serum, mucus and pus may become desiccated and 
pulverized, the field of dust infection, theoretically, 
includes not only those diseases, but also many 
others. Thus, dust infected with the pyogenic or- 



Air as 
Conveying 

Medium. 



"Dust 
Infection.* 



50 INFECTION AND IMMUNITY. 

ganisms, or with tetanus bacilli, may be derived 
from ordinary earth or earth contaminated with 
the dried excretions of animals. And in other 
cases dried and pulverized urine or feces (typhoid, 
cholera), or desiccated discharges from diseased 
surfaces, from sinus and abscesses (tuberculosis, 
erysipelas), may give rise to infected dust. The 
skin may be an important source of infected dust 
in the desquamative diseases (scarlet fever, measles, 
smallpox), in that individual horny cells or groups 
of cells laden with organisms may float in the 
air with no great velocity in the movement of the 
latter. 

The importance of dust infection is curtailed. 
however, because of the slight resistance which 
many microbes show against desiccation and the 
germicidal action of light. Gotschlich classifies 
micro-organisms regarding the likelihood of their 
participating in dust nf ection as follows : 
or^nfsms* ( a ) Organisms which are not capable of living 
in dust as it is dried in the air, and hence never 
(rarely might be better) can be disseminated 
through dried particles (cholera, plague, gonor- 
rhea, influenza). 

(b) Organisms which are capable of being car- 
ried as dust for considerable distances by such 
weak currents of air as ordinarily exist in dwell- 
ings, and which, when once suspended in the air, 
remain alive for a long time, and easily lead to 
dust infection (pus cocci, pyocyaneus, meningococ- 
cus, anthrax spores, tubercle bacilli and tetanus 
bacilli). 

(c) Organisms which, indeed, are resistant to 
desiccation, but which are disseminated as dust 
only through stronger air currents, such as occur 



DUST INFECTIOX. 51 

exceptionally in dwellings (typhoid and less often 
diphtheria). 

This leaves out of consideration the unknown conditions 
organisms of the exanthemata, referred to above. 
The conditions as they ordinarily exist in dwell- 
ings are taken as a standard, and the weight and 
size of the particles, and the velocity of the air 
in an upward direction, as well as the viability of 
the different organisms in a dried condition, are 
the essential factors which govern the likelihood 
of dust infection. "Naturally, only those infected 
particles of dried dust which may be carried up- 
ward for a considerable distance by a very low 
velocity of the air are able to remain suspended 
for some time in the atmosphere of a room and, 
consequently, exist as a protracted danger of air 
infection. M. Neisser considers as the limit that 
degree of "Verstaubbarkeit"* in which the in- 
fected particles may be carried to a height of 80 
cm. by an air velocity (upward) of 1 cm. (per 
second)." (Quoted from Gotschlich in Kolle & 
Wassermann's Handbuch der Pathogenen Mikro- 
organisms, Vol. 1, p. 168). After the dust in a 
room is once thoroughly stirred up, from one to 
eight hours are required for it to settle completely 
under the most favorable conditions (Stern, 
Fltigge, cited by Gotschlich). Dust infection may 
play a part in public buildings and conveyances 
where the currents of air are stronger than they 
ordinarily are in dwellings. Even in dwellings, 
however, the conditions are by no means uniform. 
More violent currents are excited by a breeze 
through an open window, by the movements of 
persons, and the chances of infection are increased 

* Pulverization. 



Infection. 



52 INFECTION AND IMMUNITY. 

as a consequence of "dusting." Naturally the 
longer the suspension within the period of via- 
hility of the organisms the greater the chance of 
conveyance. 
Droplet Droplets of saliva, etc., are discharged into the 
air through coughing, sneezing, laughter, and even 
forcible speaking. This does not occur with ordi- 
nary respiration. In coughing droplets may be 
carried as far as thirty feet from the individual, 
and they may be carried much farther by extrane- 
ous currents of air. Such droplets may remain 
suspended in the air for approximately an hour, 
but the period of their suspension depends on their 
size, the weight of the organisms they carry and 
the degree of moisture in the air. In a drier air 
they become desiccated more quickly and after des- 
iccation fall more rapidly. 

Laschtschenko, and also Heymann, investigated 
the dissemination of tubercle bacilli by coughing 
in pulmonary tuberculosis. In 40 per cent, of the 
cases guinea-pigs which were placed even at con- 
siderable distances from the patients contracted 
tuberculosis of the lungs or bronchial lymph 
glands. The bacilli have been demonstrated mi- 
croscopically in such droplets by numerous ob- 
servers. Leprosy bacilli are carried similarly 
(Schaffer). 

On account of their content in mucin the drop- 
Jets adhere closely to solid surfaces, where they 
soon dry and become harmless unless they are 
dislodged by some violence. 

When contained in such dry droplets the tu- 
bercle bacillus lives for about three days in the 
light and eighteen days in the dark. Most other 
organisms, except the spore-bearing and those cans- 



DROPLET INFECTIOXS. 53 

ing some of the contagious exanthemata, die more 
quickly. 

The conditions for droplet infection, then, are, conditions. 
in the main, as follows: First, the micro-organ- 
isms must be discharged into the air, in viable 
and virulent condition, and in sufficient quantity, 
from the respiratory passages of the patient. Sec- 
ond, they must be able to retain life and virulence 
for a greater or less period of time, after 
being liberated in this way. Third, they must be 
able to use some portion of the respiratory tract, 
or the gastro-intestinal tract indirectly from the 
respiratory tract, as an infection atrium. Fourth, 
the advent of a susceptible person within the zone 
of infected atmosphere which surrounds the pa- 
tient during the period of viability and virulence 
of the excreted organisms. 

In general the same principles also apply to dust 
infection so far as it concerns the ordinary "air 
borne" diseases. 

The question is commonly raised as to which Relative 
is the more important, or more prevalent, dust in- 
fection or droplet infection. Although it is the 
tendency at present to assign a minor role to dust 
infection, it unquestionably is of importance in 
certain diseases, particularly in tuberculosis. The 
situation may be conceived to be as follows : In 
relation to diseases caused by micro-organisms 
which have little resistance to desiccation and 
light (e.g.., plague, influenza), droplet infection, 
implying proximity to the patient, is more likely 
to occur than dust infection (as in occupying a 
room vacated by a patient a longer or shorter pe- 
riod previously). Concerning those caused by or- 
ganisms which have greater resistance to desieca- 



54 INFECTION AND IMMUNITY. 

tion and light, as in tuberculosis, the importance 
of dust infection approximates, though it may not 
equal, that of droplet infection. 
water as Just as the air is the principal medium of con- 
Medium, veyance for the group of diseases discussed above, 
so contaminated water plays an important, but not 
the sole, part in the transmission of another group. 
Typhoid and paratyphoid fever, cholera and bacil- 
lary dysentery are the chief representatives. 

Epidemics which arise in this way are frequently 
spoken of as "water-borne" epidemics. Sometimes 
typhoid and cholera are called "water-borne" dis- 
eases, but epidemics are so often instituted and 
maintained by various kinds of indirect contact 
. that the appellation is one-sided. 

conditions. Three essential conditions are required in order 
that a disease may be more or less habitually 
transmitted through water : First, the discharge 
of the organisms from the body of the patient in 
such form that they may reach a water supply. 
Second, the ability of the organisms either to live 
for a moderate length of time in the water, or to 
proliferate in it, without losing virulence. Third, 
the utilization of the gastro-intestinal tract, the 
upper respiratory tract, or the lungs indirectly 
from the latter, as an atrium of infection. 

The first condition is readily realized in the dis- 
eases mentioned, inasmuch as the micro-organisms 
are discharged in large numbers with the feces, 
and also, in the case of typhoid and paratyphoid, 
with the urine. 

contamina- ^ types of water supplies may be contaminated 
tion. by these excretions. When the water of a com- 
munity is taken from a stream the latter may be 
infected by the sewage of another community 



VIABILITY IN WATER. 55 

higher up the stream, or by the discharges of even 
a single patient. The throwing of typhoid dis- 
charges on the bank of a stream has resulted in 
severe epidemics. Reservoirs may be infected sim- 
ilarly. In some instances a city which derives its 
water from an inland lake also empties its sewers 
into the same body of water. Even when the sew- 
age outlet is quite remote from the water intake, 
surface currents, as caused by the wind, may carry 
water, and hence infection, from the former to the 
latter. In harbors the water may become infected 
from the sewage of a ship which carries a case of 
cholera. Streams have been contaminated by 
washing in them the soiled linen of patients. When 
excretions are thrown on the ground the micro- 
organisms have been carried into wells by surface 
water from which small epidemics have arisen. 

The very occurrence of water-borne epidemics viability 
indicates that the micro-organisms concerned live 
for a longer or shorter period of time in ordinary 
waters. Various factors influence their longevity 
in water, and their persistence at the point of first 
contamination. Purer waters are not so favorable 
for the life of the organisms of typhoid and chol- 
era, as those which contain a certain amount of or- 
ganic matter and salts. On the other hand, an ex- 
cess of organic matter when accompanied by many 
saprophytic organisms also shortens the life of 
these bacteria, particularly when in stagnant 
water; and this principle is utilized for purifica- 
tion of sewage in those systems which involve the 
use of sewage tanks. A rapidly flowing stream 
naturally results in purification more quickly than 
one which is sluggish. 



Water 



56 



INFECTION AXD IMMUNITY. 



"Water- 

tiorne" and 

"Contact" 

Epidemics. 



Conveyance 
by Pood. 



Data regarding the longevity of these organisms 
in water and milk are given in the sections on 
cholera and typhoid. 

"Water-borne" epidemics are characteristic in 
this, that very many individuals are stricken sud- 
denly and simultaneously and the outbreak is, at 
first, limited to those who are supplied by the in- 
fected water. "Contact" epidemics, on the other 
hand, progress slowly and irregularly, although 
they may finally reach large proportions. Nat- 
urally an epidemic begun by contaminated water 
may be maintained by contact, and continuance by 
contact again offers opportunity for the fresh in- 
fection of water, milk and food. The viability of 
micro-organisms in the excreta, after the discharge 
of the latter, is important, both from the stand- 
point of water infection and that which occurs 
by indirect contact. Uffelmann determined that 
typhoid bacilli may live in the dejecta for many 
months, and, at least under some conditions, the 
cholera vibrios in the feces is viable for two or 
three weeks (Lubarsch) . 

As stated previously, diseases which are peculiar 
to man may be distributed by milk which has been 
contaminated by convalescents (as in scarlet fever) 
or by "carriers," or by some others indirectly from 
these, or by infected water used in washing con- 
tainers. Epidemics caused by infected milk are, 
in miniature, similar to those arising from a con- 
taminated water supply, their distribution coin- 
ciding with the area of consumption of the milk. 

Other food substances act as carrying agents 
only when they become infected accidentally, as by 
flies, washing in contaminated water, or by con- 
valescents and "carriers." 



CONVEYANCE BY CLOTHING, ETC. 57 

Transmission by direct and indirect contact are contact. 

somewhat in contrast. In the former actual per- 
sonal contact takes place between the sick and 
health} 7 , as previously stated, and as illustrated by 
gonorrhea and syphilis.* Probably many of the 
infections which are conveyed through the air may 
also be acquired by direct contact. However, a 
distinction in this case has no significance, since 
actual contact without exposure to air infection 
could hardly occur. 

Indirect contact, on the other hand, implies 
transmission through the agency of an interme- 
diate person or object. Speaking strictly, convey- 
ance from person to person, through the air, water, 
or even by insects, comes within the domain of in- 
direct contact, yet their methods are so specialized, 
so obtrusive and so constantly utilized by certain 
groups of micro-organisms that they deserve the 
separate consideration usually given them. The 
tendency is a correct one to withdraw from the 
domain of indirect contact any method of trans- 
mission which can be spoken of more concretely. 

One could not hope to mention all of the possi- 
ble channels through which an infection may be 
carried indirectly. There are great variations in 
details. "Carrying a disease in one's clothing" 
from place to place; the use of the toys of a diph- 
theritic child; washing or handling the linen of a 
cholera, typhoid or dysentery patient; occupying a 
room formerly used by a patient having scarlet 
fever or tuberculosis; the occasional transfer of 
syphilis by the drinking-cup or the dentist's for- 

* Exceptions occur in relation to syphilis, as in the oc- 
casional transfer by drinking cups and instruments ; 
hereditary syphilis may be considered as a special case. 



53 INFECTION AND IMMUNITY. 

ceps; the former occurrence of contagious hospital 
gangrene through contamination of dressings and 
of other infections from patient to patient through 
unclean instruments or hands; these are examples 
of conveyance by indirect contact. 

As some of them show, diseases which are ha- 
bitually transmitted through the air (scarlet fever) 
or by water (typhoid, cholera) may also be trans- 
ferred by indirect contact. 
Hereditary In the strict zoological sense no form of trans- 
sion. mission of an infection from parent to offspring 
can be viewed as truly hereditary, since inheritance 
concerns only properties which are inherent in the 
germ cells and their chromatin. Micro-organisms 
are foreign and their introduction in the germ 
cells from the parent can only be considered as 
accidental. It is, then, only for the sake of con- 
venience and for lack of a more exact term that 
the inheritance of infections is spoken of. Tins 
distinction has been strongly emphasized by Han- 
sen (Virch. Arch., Vol. 120) and by Lubarsch 
(Ibid., Vol. 124). Some of the metabolic diseases 
and functional derangements, on the other hand, 
may be truly inherited, or, perhaps better, a ten- 
dency or predisposition to them may be inherited. 
Also, it is very probable that susceptibility, or, on 
the other hand, resistance to some particular infec- 
tion, may be inherited, thus accounting for the 
frequent or rare occurrence of some infections in 
a given family. 
Germ Ceii When disease of the offspring can be referred to 
infection. a p r i mar y invasion of the germ cells (ovum or 
sperm cells) by micro-organisms it is said to have 
originated by "germ cell infection/' It is not 
definitely known that this type of hereditary trans- 



GERM CELL INFECTION. 59 

mission takes place in man, and the likelihood of 
its occurrence could be proved only by finding the 
micro-organisms actually within the ovum of 
sperm cell. 

Definite examples of this type of transmission 
are found in insect life, particularly among ticks. 
The piroplasmas of Texas fever and of Ehodesian 
fever of cattle, the spirillum of South African 
tick fever of man, and the virus of Eocky Moun- 
tain spotted fever are all transmitted to the lar- 
vae of the next generation through infection of 
the ova of the corresponding ticks. 

Since it does occur in other forms of life, it 
would not be surprising if it also occurs in man. 
In that form of inherited syphilis in which the 
child derives the infection from the father, the 
mother apparently remaining uninfected, the virus 
may have been introduced into the ovum by means 
of an infected sperm cell. Even in this case, how- 
ever, it is virtually impossible to rule out the exis- 
tence of a latent infection of the mother. And if 
such infection does exist, the spirochetes may have 
reached the embryo by way of the placenta, in- 
stead of through the ovum. Possibly the recently 
discovered test for syphilis (fixation of comple- 
ment) will throw some light on this phase of in- 
herited syphilis, since it renders possible the diag- 
nosis of the disease in the mother regardless of 
positive clinical manifestations. 

It is equally, or perhaps more, uncertain as to 
whether tuberculosis is ever inherited through in- 
fection of the germ cells. Tubercle bacilli have 
been found in the testicular secretion in both man 
and animals. In such cases the tuberculosis is of 
an advanced type, resulting in early death. Even 



Transmis- 
sion 



60 INFECTION AND IMMUNITY. 

if some of the bacilli were actually within the 
sperm cells and capable of introduction into the 
ovum through them, the great preponderance of 
the spermatozoa over the bacilli renders infection 
of the ovum improbable. In one such case Gartner 
estimated the numerical relation of the bacilli to 
the spermatozoa as one to 22.7 million, hence the 
impregnating cell would very likely be an unin- 
fected one. 

It has sometimes been assumed that leprosy may 
be transmitted in this way, but there is no strong 
evidence in support of it. 
placental Infection of the embryo, from the mother, by 
way of the placenta, has been demonstrated experi- 
mentally, and encountered clinically, unmistakably. 
Opinions differ as to whether actual involvement 
— i. e., infection or defects — of the placenta is 
prerequisite to the passage of micro-organisms 
from the mother to the embryo. 

M. Wolff, on the basis of experimental work with 
the anthrax bacillus, concluded that the uninjured 
placenta, is an effective barrier against such a 
transfer. It was supposed, however, that injuries 
of the placenta which resulted in bleeding, thus 
establishing a temporary connection between the 
circulations of the mother and fetus, as well as 
other lesions metastatic in character, could well 
result in infection of the embryo. Many others 
also, on the basis of experimental work and the 
study of human material, concluded that there 
must be recognizable lesions of the placenta to 
permit transfer from mother to child. The bacil- 
lus of chicken cholera, a member of the hemor- 
rhagic septicemia group of organisms, causes hem- 
orrhages in the placenta in animals and is trans- 



PLACENTAL TRANSMISSION. 61 

mitted to the embryo (Malvoz). Tuberculosis oc- 
casionally, and syphilis very often, attack the pla- 
centa in man. In a number of instances fetuses 
have been born with the eruption of smallpox 
derived from the mother and the transfer of ty- 
phoid bacilli through the placenta has been ob- 
served occasionally. Similar transmission in man 
has been noted in relation to anthrax, pneumonia, 
recurrent fever, and infections with the pyogenic 
cocci. Abortions, due either to infection or intox- 
ication, may occur during most of the acute fe- 
brile infections. 

Contrary to the view expressed above, Baum- 
garten, Birch-Hirschfeld, Lubarsch and many 
others conceived that a pre-existing injury of the 
placenta is not essential for transfer; that the 
micro-organisms, especially when present in the 
blood in considerable numbers, as in anthrax, may 
"grow through" the placental vessels in the absence 
of, and without causing, anatomical lesions. 

It is extremely probable that both views are cor- 
rect, but perhaps in relation to different types of 
micro-organisms. It has been demonstrated many 
times, clinically and experimentally, that tubercle 
tfacilli will pass through the intestinal mucosa into 
the adjacent lymphatics without causing lesions 
of the mucosa, and, although the conditions are not 
identical in the two structures (migration of wan- 
dering cells through intestinal wall!), the occur- 
rence in one suggests its possibility in the other. 
However, the existence of the phenomenon is so 
thoroughly established as to render the exact mech- 
anism a more or less secondary matter. 

It is an important theory of Baumgarten's that latent 
tubercle bacilli which are acquired during fetal infection. 



62 INFECTION AND IMMUNITY. 

life may remain latent until puberty and then, 
when the unusual resistance which is coincident 
with rapid growth has subsided, the bacilli mul- 
tiply and tuberculosis manifests itself. He sup- 
poses also that an intermediate generation may, 
without showing tuberculosis itself, transmit the 
disease to the next generation (U eber spring ling von 
Generationen) . This would seem to presuppose 
the occurrence of germ-cell infection, but perhaps 
not necessarily so. As having a possible bearing 
on Baumgarten's hypothesis, it has been found by 
Harbitz, by Wechsefbaum and others that tubercle 
bacilli, particularly in children, may exist in the 
lymph glands without causing anatomical changes. 
This view has several strong supporters, and it 
is thought that the bacilli may remain latent in 
any portion of the body. That hereditary syph- 
ilis may remain latent for many years is well 
known. 

On the other hand, it is more generally believed 
that tuberculosis in most instances is a postnatal 
acquisition (Koch, Cornet and others) and ra- 
tional prophylaxis naturally must be based on this 
conception. Extensive involvement of the liver 
and periportal lymph glands is characteristic of 
the placental transmission of tuberculosis. The be- 
lief is occasionally expressed that leprosy may be 
inherited, possibly through placental transmission, 
but, in view 7 of the non-susceptibility of animals 
and failure to cultivate the bacillus, the question 
cannot be taken up experimentally. The possibil- 
ity of infection of the embryo directly from the 
father during coitus is discussed, but there is no 
definite proof of its occurrence. 



HEREDITARY INFECTION. 63 

It is conceivable that micro-organisms may pass 
from the mother to the child by way of the blood 
through the placenta at the inception of labor dur- 
ing an early stage of separation of the placenta 
from the uterine wall. 

Infection of a child, as with gonorrheal ophthal- 
mia, during delivery is not regarded as an ex- 
ample of "inheritance" of disease. It is an extra- 
uterine process, a congenital infection. 



CHAPTEE VI. 



SOURCES OF PATHOGENIC MICRO-ORGANISMS 

(Concluded.) 

(6) Dissemination and Transmission by Insects. 

A. Dissemination. 

Role of The demonstration that insects may play a role 

insects. ^ n ^ e transmission and maintenance of infections 

dates from the work of Smith and Kilbourne, 

which disclosed the relation of the tick (Margaro- 

pus annulatus) to Texas fever in cattle. 

Insects may act simply as disseminators of 

virus, or as the agents of actual inoculation 

through their bites — i. e., as transmitters. It is 

important to keep this distinction in mind. 

Bioiog-ic and i n their role as pure disseminators they may 

Mechanical . . „ . 

Transmission, carry micro-organisms from one point to another 
on their feet, mouth parts, or in their intestinal 
contents ; or, they may act as temporary hosts, the 
microbes proliferating in their intestinal tract and 
subsequently being deposited with the feces, in in- 
creased numbers, at some new point. The first is 
pure mechanical dissemination, whereas in the sec- 
ond a biologic factor enters, that of proliferation, 
and it may be spoken of as biological dissemina- 
tion. For example, when flies carry typhoid bacilli 
or cholera vibrios from feces to food, on their feet 
or mouth parts, or tubercle bacilli from sputum to 
food or other objects, this is, of course; a purely 
mechanical process. It would be complicated by 
the biological feature, however, in case the or- 



FLY TRANSMISSION. 6.3 

ganisms, after ingestion by the fly, then multi- 
plied, and were deposited in larger numbers in 
fly-specks. It is, indeed, a difficult point to deter- 
mine whether or not proliferation of these micro- 
organisms actually takes place in the intestines of 
the fly. Observations by Spillman and Haushalter, 
Hofmann, Celli, Hay ward, Lord and others have 
shown conclusively that house-flies ingest tubercle 
bacilli from the sputum of patients and excrete 
them in their feces. The observations of Lord 1 
suggest, but do not actually prove, that the bacilli 
multiply in the intestines. It has been demon- 
strated several times, by inoculation into guinea- 
pigs, that the bacilli in the fly-specks are virulent. 
The specks dry quickly and there is little danger 
of the organisms taking part in dust infection un- 
less the specks are violently dislodged, and they 
die in a few days. On the other hand, there may 
be a real danger from the deposition of the specks 
on food (Lord), which suggests a point in pro- 
phylaxis. 

Similar questions are raised also in the relation 
of the fly to typhoid, cholera, dysentery and plague. 
The importance of the fly in the mechanical dis- 
semination of typhoid bacilli, resulting in exten- 
sion of epidemics, is now well established, as illus- 
trated by the observations of Alice Hamilton, and 
the inquiry into the prevalence of typhoid fever 
in the American troops during the Spanish- Amer- 
ican war. The conditions are similar in relation 
to cholera. Concerning dysentery it is considered 
probable that flies are a factor in distribution, al- 
though the point has not been positively demon- 
strated. It is uncertain whether the organisms of 

1. Reports of the Massachusetts General Hospital. 



66 INFECTION AND IMMUNITY. 

typhoid and cholera proliferate in the intestines of 
the fly. It seems not unlikely in the case of ty- 
phoid, inasmuch as Ticker 2 found them in the fly 
twenty-three days after a feed on the bacilli. Tsu- 
zuki 3 cultivated cholera vibrios from flies which 
were taken in the dwellings of patients. 

It seems probable that flies, in some instances, 
may distribute plague bacilli after they have them- 
selves become infected by feeding on the sputum 
of pneumonic patients or on the cadavers of rats 
dead of the disease. Yersin 4 found plague bacilli 
in flies dying in a laboratory in which plague was 
being studied, and in NuttalPs 5 experiments they 
became infected by feeding on diseased organs. 
The Flea and The flea, on the other hand, appears to act both 
as a disseminator and as a transmitter of plague. 
The human flea, at least two species of rat fleas. 
and the flea of the dog and cat readily become in- 
fected by feeding on rats during the stage of septi- 
cemia in the latter, the bacilli multiply for a few 
days in their stomach and intestines, and are ex- 
creted in large numbers in their feces. They are 
able to communicate the disease to other animals 
by biting for at least three days after their infec- 
tion, but in a short time the bacilli disappear from 
their alimentary tract and they lose the power of 
transmission. The organisms, which are excreted 
in their feces, are virulent, and are able to produce 
infection through very small abrasions and 
through the minute wounds made by the bites of 
these insects. The deposition of bacilli in the feces 
of the flea on the skin of a person is a question 

2. Arch. f. Hyg., 1903, xlv, 247. 

3. Arch. f. Schiffs-u. Tropenhygiene, February, 1904, viii 

4. Ann. de l'Inst, Past., 1904, i, 662. 

5. Centralbl. f. Bakteriol., 1897, Abt. I, xxii, 87. 



IX SECTS AXD PLAGUE. 67 

of dissemination, whereas the injection of the or- 
ganisms through the proboscis is one of inocula- 
tion. The flea appears not to undergo a gen- 
eralized infection with the plague bacillus. 

It is possible that rats may become infected 
with plague also by the eating of fleas which con- 
tain bacilli, although this has not yet been demon- 
strated. Experimentally the disease has been pro- 
duced in rats by feeding them infected tissues or 
cultures. 

Yerjbitski also found that the bedbug behaves in Tlie Bedbug. 
a manner exactly similar to the flea in the case of 
plague. In actual epidemics, however, it seems 
probable that this insect would be concerned only 
in the transmission of the disease from man to 
man, and not from rat to man. 

With the exception of the last paragraph the 
above concerns the mere dissemination of micro- 
organisms by insects. As noted, the diseases con- 
cerned are bacterial in nature rather than proto- 
zoan. Pathogenic protozoa may be excreted by in- 
sects, but, if so, the event appears to be without 
practical significance, either because the organisms 
are not viable when excreted, or are not in a stage 
of development to render them infective, or, what 
is more probable, that they find no infection 
atrium when in this condition. Those protozoa 
which are transmitted by insects usually require 
actual inoculation in order that they may cause 
infection. 

B. Transmission 

Our knowledge is by no means complete on 

the subject of insect transmission, as a whole, al • 

though the essential facts have been worked out 

in a number of instances, as in Texas fever, some 



6S INFECTION AND IMMUNITY. 

other piroplasmoses, and in malaria. In some in- 
stances it is the micro-organism which is unknown 
(yellow fever, dengue), in others the question of 
inheritance in the insect (trypanosomiasis), in 
others the relation of the insect and the disease to 
hosts other than man, etc. 
Transmitted Diseases which are transmitted habitually, or 
i»y insects, mainly, by insects sometimes possess rather dis- 
tinctive epidemiologic features. Malaria occurs in 
swampy regions in which certain species of Ano- 
pheles abound. The distribution of yellow fever, 
and indeed of all the insect-borne diseases, coin- 
cides with that of the insects which are concerned 
in the distribution. In the temperate and subtrop- 
ical countries such diseases tend to prevail in the 
warmer months and to disappear on the advent 
of frost or cooler weather, an event which is cor- 
related with the activity or inactivity of the insects 
during these seasons. The Indian plague commis- 
sion finds that an epidemic wanes when the mean 
daily temperature is below 50° F., presumably be- 
cause the flea does not become infected so readily 
under this condition : the rats die before the advent 
of intense septicemia, and without the latter the 
flea is less likely to become infected. The flea 
may also be less likely to feed generously in the 
cooler weather. Also it was found that a mean 
daily temperature of 85°-90° F. coincides with the 
decadence of an epidemic, and in harmony with 
this it appears that the flea remains infective for 
a much shorter time at this temperature. When 
virtually all the rats of a locality have either 
been killed by plague, or have recovered from it, 
those which remain are for the most part 
immune, and the conditions for a recrudescence 



IN SECT TRANSMISSION. 69 

of an epidemic will not be ripe until a new gen- 
eration of rats has been bred. The immune 
rats do not harbor plague bacilli, and hence 
cannot infect fleas. Eocky Mountain spotted 
fever prevails only in the months of spring. At 
this time the tick which acts as transmitter is in 
its adult stage and readily feeds on man as well as 
on other animals. The larval and nymphal stages 
appear at other seasons, and, although their bites 
are infective, they rarely feed on man, either from 
lack of opportunity or because of a preference for 
other hosts during these stages. The observation 
of Carter, that when yellow fever patients are first 
imported into a new district a definite period 
(two to three weeks) elapses before new cases de- 
velop, suggested some novel mode of transmission, 
which eventually was proved true when Seed, Car- 
rol and Agramonte proved by experimentation the 
correctness of the mosquito theory of Carlos Fin- 
lay and worked out the details of transmission. 

For some time it was supposed that insects 
transmit only those diseases which are caused by 
protozoan organisms. This impression arose from 
the fact that the first examples of definitely proved 
insect transmission concerned protozoan diseases, 
as Texas fever (a piroplasmosis) of cattle, malaria 
of man and birds, and more recently the try- 
panosomatic diseases. It is only since the rela- 
tionship of the flea to plague, of the tick to the 
South African tick fever of man, and of other 
mites to spirilloses of animals that the importance 
of insects in transmitting bacterial diseases has 
been recognized. contagions- 

T . . . . . ness Simn- 

It is an interesting fact that contagiousness is latea by in- 
sometimes simulated in a disease which is trans- mission. 



Sources of 



70 INFECTION AND IMMUNITY. 

mitted only by insects. Thus, for many years, yel- 
low fever was held to be so contagious that not 
only direct transfer from person to person was 
admitted, but also through various indirect means 
as by fomites. Typhus fever has often been cited 
as the most contagious of all infections, yet mod- 
ern studies point rather strongly to an exclusive 
insect transmission (perhaps fleas or bedbugs). 
The conditions in plague seem to be somewhat 
more complex, in that both insect transmission 
(fleas) and contagiousness prevail, the latter com- 
ing into play in the pneumonic form of the dis- 
ease. Dengue, which spreads like wild fire, pos- 
sibly is transmitted only by the bites of certain 
mosquitoes. 

In some instances the role of the insect is an ob- 
ligate one — i. e., transmission can occur in no other 
way than by its bite. This is pre-eminently true 
of malaria, which, virtually, is incapable of trans- 
mission from person to person even when malarial 
blood is injected into a healthy person. The par- 
asite when it leaves the body becomes infective for 
man again only after it has completed a sexual 
development in the mosquito. In some instances 
infection may be carried from person to person 
or animal to animal by the injection of diseased 
blood, yet under natural conditions the role of the 
insect is an obligate one (yellow fever, sleeping 
sickness, Eocky Mountain spotted fever). The 
flea in plague transmission is an example of a 
facultative role, since, as stated, this insect is not 
the only natural means by which the disease is 
conveyed from person to person. 

Insects which carry and transmit infections nat- 



Enfection. urally must have some source from which they 



SOURCES OF INSECT INFECTION. 71 

derive the micro-organisms. Commonly, the trans- 
mission occurs only between different members of 
the same species : the insect obtains the virus from 
one individual and inoculates it into another. In 
so far as is known, man alone suffers from yellow 
fever, and the human type of malaria, and he 
constitutes the only source of infection for the 
mosquitoes which are concerned in the mainte- 
nance of these diseases. The same conditions ap- 
pear to prevail regarding piroplasmosis in cattle 
(Texas fever) and in other animals, and also in 
the South African tick fever of man (a spirillosis), 
diseases in which ticks are transmitters. Pre- 
sumably this is also true of some other insect- 
borne diseases among animals, as the spirillosis of 
fowls and geese. 

In some other instances the existence of a third 
host has been demonstrated. Man is an important 
source of infection for the flies which carry sleep- 
ing-sickness, but the evidence is strong that some 
of the native animals of Africa also harbor the 
trypanosome concerned and that tsetse flies be- 
come infected from them as well as from man. In 
Rocky Mountain spotted fever man is virtually a 
negligible factor for the infection of the ticks. 
The circumstances indicate that one or more spe- 
cies of small, wild animals, of demonstrated sus- 
ceptibility, are the means of keeping the diseases 
alive in the ticks. It appears to play back and 
forth from tick to animal, and it is only occa- 
sionally that an infected tick becomes attached to 
man. Fleas probably derive the micro-organisms 
of plague from rats, in large measure, but experi- 
ments also show that they may become infected 
from man. 



72 INFECTION AND IMMUNITY 

Aside from the sources mentioned, the possibil- 
ity also exists, in relation to some infections, that 
the viruses are native to the insects, or, rather, 
that they are habitual parasites in them, just as 
the colon bacillus is a constant inhabitant of the 
intestinal tract of man. Even in this case, how- 
ever, we must assume either some extraneous 
source for the organisms or that they are inherited 
from the preceding generation of insects. The lat- 
ter, indeed, is a method of acquisition which has 
been shown to occur in ticks, in relation to the 
Texas fever of cattle, and the South African tick 
fever, and Rocky Mountain spotted fever of man. 
The eggs of infected females contain the respective 
micro-organisms and the larvae which hatch from 
them are infective. 
Factors in The factors which enable an insect-borne disease 
M oi n msease! to De maintained from year to year vary a good 
deal in different cases. Chronicity, in either the 
animal or insect host, or in both ; inheritance of 
the disease in the insect, and a rapid alternation 
of the infection between the insect on the one hand 
and the animal host on the other — these seem to 
be the important conditions which have a bearing 
on maintenance in one disease or another, and all 
of them assure a more or less constant source for 
the fresh infection of the carriers. 

Texas fever of cattle and other piroplasmatic 
infections, malaria, and sleeping-sickness are 
chronic infections in both the animal and insect 
hosts. Each exists as a more or less protracted 
source of infection for the other. In addition, 
Texas fever, and some other piroplasmoses, are 
hereditary infections in the tick-carriers, and in 
this way infection is readily kept alive, from one 



ROCKY MOUXTAIX FEVER. 



73 



season to the next. It is not yet known whether 
sleeping-sickness is inherited in the tsetse fly. Ma- 
laria is not so transmitted in the mosquito. 

There may be varying grades of chronicity in soatii African 
both the animal and insect hosts. Thus South Af- 
rican tick fever of man (a spirillosis) is semi- 
chronic, consisting of several recurrences followed 
by recovery, and it is probable that the tick maj 
acquire the disease from the patient during any 
one of the recurrences. In the tick, however, the 
disease is chronic and hereditary. 

In these cases the method of maintenance is 
clear, and in the presence of a sufficient number 
of insects the conditions are favorable for a 
thorough infection of the inhabitants. Thus it is 
that in many tropical districts there are none who 
do not fall victims to malaria sooner or later. 

In Eocky Mountain spotted fever we have an 
example of a condition in which the disease is 
acute in the various animal hosts, including man, 
but chronic in the carrier, the tick. In order that 
fresh ticks may acquire the disease it is necessary 
for them to feed on a susceptible animal in com- 
pany with infected ticks, or shortly following a 
feed by the latter. Since several hundred larva? 
or nymphs may be found on one of these animals 
at the same time, it is readily seen how this may 
be accomplished. While certain of the small ani- 
mals (ground-squirrel, ground-hog, rock-squirrel, 
and perhaps others) are in hibernation the 
virus still lives in the eggs, larva? and nymphs; 
and when the animals "come out" in the spring 
certain of them become infected through the bites 
of the larvas or nymphs and then are in condition 
to infect fresh ticks. Hence the disease is kept 



Rocky Moun- 
tain Spotted 
Fever. 



74 INFECTION AND IMMUNITY. 

alive through inheritance in the tick during the 
months of winter, and at other times through 
alternation from tick to animal and animal to tick. 
Man plays little or no role in its maintenance, and 
his occasional infection through the tick bite may 
be regarded, in a sense, as an unessential incident. 

Yellow fever, again, illustrates the condition of 
an acute infection in the animal host (man) and 
a chronic in the insect (Stegomyia calopus). 
Like Eocky Mountain spotted fever, the virus of 
yellow fever is transmitted in a hereditary man- 
ner to the next generation of mosquitoes (Mar- 
choux and Simon d) in some instances at least. 6 
piag-ue Th e conditions in plague are peculiar in that the 
disease runs an acute course in both the animal 
hosts (rats and man) and in the insect trans- 
mitter (flea). Eats do indeed surfer from chronic 
plague in some instances, but this is not a septi- 
cemic condition, hence it affords little or no oppor- 
tunity for the infection of fleas. 

It may be questioned whether the presence of 
plague bacilli in the stomach and intestines of the 
flea constitutes a true infection, but it seems justi- 
fiable to take this view of the condition, since the 
bacilli apparently proliferate in this locality for a 
few days at least (Verjbitski). Verjbitski found 
that fleas will transmit plague for three days after 
their infection, the Indian plague commission for 
from eight to twenty-one days depending on the 
temperature at which the insects had been kept — 
for twenty-one days at 75° -80° F., for eight days 

6. The British commission also appears to have been suc- 
cessful in proving this hereditary transmission, although the 
attempt had failed in the hands of Reed, Carrol and Agra- 
monte, and of Rosenau and Goldberger. Possibly it occurs in 
only a small percentage of the insects. 



HEREDITY OF INSECT INFECTION. 75 

at 90° F. These findings also correspond with the 
bacteriologic examination of the intestinal and 
stomach contents. Verjbitski's work in relation 
to the bedbug and plague was referred to above. 

Although plague is acute in both the animal 
and insect hosts, maintenance is facilitated 
through the large numbers of both hosts which 
are present in plague centers. The conditions 
render possible a more or less permanent source 
of infection for the fleas through the continued 
infection of fresh rats. The possibility also exists 
that the chronic nodular plague of rats may be 
subject to exacerbations, accompanied by septi- 
cemic infection, a condition which would afford 
opportunity for the further infection of fleas. It 
has recently been shown by the work of Wherry 
and others that the California ground-squirrels 
have played a part in the persistence of plague in 
that region, a discovery which may have profound 
epidemiologic importance for the United States. 

Inheritance in the insect has been mentioned as 
a factor in the maintenance of Texas fever, Af- 
rican tick fever of man, yellow fever and Eocky 
Mountain spotted fever. Schaudinn also found 
that the mosquitoes which carry Trypanosoma noc- 
tucB (the "halteridium" of the stone owl) pass the 
micro-organisms to the next generation through 
the eggs. In Texas fever this appears virtually to 
be the sine qua non for maintenance in view of the 
peculiar habit of the tick of going through its vari- 
ous stages of development on the host to which 
the larvse first become attached. 7 In order to make 

7. Most ticks pass through three active stages in their 
development. The freshly engorged and impregnated female, 
after a period of rest, lays a great many eggs. Following 
an incubation period 6-legged larvse emerge from the eggs, and 



76 INFECTION AND IMMUNITY. 

this point clear, let us assume that the disease is 
not hereditary in the tick. Let some normal larva? 
become attached to an infected steer. They might 
acquire the disease from this animal, but could 
play no part in the infection of others, since they 
do not abandon this host until they have reached 
the adult stage and the females are prepared to 

immunity, lay eggs. The latter then drop and lay their eggs, 
and, in accordance with our assumption, the larvae 
which emerge would not have the power of infect- 
ing further animals. In this case the tick would 
be a factor in maintenance only in the event that 
infected individuals should through accident be- 
come dislodged from one host and subsequently 
become attached to a susceptible animal. This 
may occur in some instances. 

East coast The conditions are different in the case of 
another piroplasmosis of cattle, namely, the 
Ehodesian or East Coast fever, which occurs in 
Africa. In this case, as determined by Lounsbury 
and by Theiler, the brood from an infected female 
is not infective, but larva?, when fed on diseased 
blood, are infective after reaching the nymphal 
stage, and, likewise, when infected as nymphs the 
adults have the power of transmission (Rhipi- 
cephalus appendiculatus) . This is known as stage- 
to-stage infection, and is important in this in- 
stance, inasmuch as the larvae and nymphs leave 
the hosts to molt. Following the molt they f re- 
soon become attached to hosts. Then they feed, pass into a 
quiescent stage, and leaving a white skin, appear as 8-legged 
nymphs. These also feed, become quiescent for a period, and 
casting off a white skin are now adults, which are differ- 
entiated sexually. In some instances, as in the tick trans- 
mitting Texas fever, both molts occur on the host. More fre- 
quently, however, other species leave the host to molt. From 
several weeks to several months are required for the whole 
cycle. 



Fever. 



INHERITANCE OF PIROPLASMAS. 77 

quently reach susceptible hosts, and thus keep the 
disease alive. Koch, perhaps in dealing with 
another species of tick (Rhipicephalus decolora- 
tus), found that hereditary transmission of 
Ehodesian fever does occur. 

Piroplasmosis of the dog presents still another 
interesting condition in regard to inheritance in 
the tick. Neither the larvae nor the nymphs of 
an infected female are able to produce the disease, 
but when they reach the adult stage they become 
infective. It has been assumed that the period 
between the egg and the adult stage is required by 
the micro-organism for the completion of its sex- 
ual evolution, the latter being necessary before it 
could again become infective. 8 This tick also leaves 
its host to molt, hence the adults are able to infect 
new hosts, and from the latter fresh ticks may 
again become infected. The disease is frequently 
chronic in the dog as well as in the tick. Motas 
found that the tick Rhipicephalus bursa, behaves 
in a similar way in the transmission of piroplas- 
mosis of sheep. In this instance the tick remains 
on the host for the first molt, but leaves it for the 
second. An infected brood is able to transmit the 
disease only after it reaches the adult stage. 

Christophers has reported still another variation 
in the inheritance of piroplasmas, in the case of 
Piroplasma canis in India. The tick concerned in 
this instance was Rhipicephalus sanguineus, which 
leaves its host for both molts. The larva? of an 
infected brood are not virulent, but become so 
when they reach the nymphal and adult stages. 

8. Experiments by Lounsbury with the tick, Hwmaphy- 
salis leachi. 



78 INFECTION AND IMMUNITY. 

Eocky Mountain spotted fever not only is inher- 
ited in the tick, but both larvae and nymphs may 
acquire the disease by feeding on infected blood 
and transmit it by biting when they reach the sub- 
sequent stage. Hence both hereditary infection 
and stage to stage infection occur in this case. 

It is questionable whether any disease can be 
maintained in an insect indefinitely through inher- 
itance alone. Mollers 9 found that South African 
tick fever could be carried into the third genera- 
tion of ticks (Omiihodoros mouboia), neither the 
second nor third generation of ticks having had 
opportunity to suck diseased blood in the mean- 
time. The experiment was not carried beyond this 
point. In relation to Eocky Mountain spotted 
fever not more than 50 per cent, of the infected 
females transmit the infection to their offspring, 
hence maintenance through inheritance alone is 
considered as impossible. 

Certain considerations relative to the course of 
infection in insects, the incubation period which 
may intervene between the moment of their inocu- 
lation and the appearance of infectivity, and, in 
addition, the duration of their infectivity, are of 
interest and importance. These points may be 
discussed briefly and only in a general way. 
innocuous- ■ It is striking that diseases which are trans- 
»«e°Germs mitted by insects appear to have little pathogenic 
carrier* influence on the insects themselves. The malarial 
Plasmodia penetrate the wall of the stomach, reach 
the body cavity and eventually the salivary glands, 
and this, it would seem, without compromising 
seriously the health of the mosquito. The flea 

9. Ztschr. f. Hygiene, 1907, lviii, 277. 






PERIODS OF INFECTIVITY. 79 

harbors in its alimentary tract for several days 
or weeks the most virulent plague bacilli, but 
eventually they are cleared away. In those in- 
stances in which hereditary transmission occurs, 
as in piroplasmosis, South African tick fever, and 
Eocky Mountain spotted fever, the eggs may con- 
tain large numbers of the specific micro-organisms 
and yet give rise to apparently healthy larvae, 
which are able to pass through the successive 
stages into the adult form, still retaining the viru- 
lent micro-organisms in their organs and cells. It 
is probably by virtue of this bland relationship 
that insects are able to figure as the carriers of 
infection. If the latter were more virulent for 
the insect hosts it is fair to assume that their 
death in large numbers would minimize their role 
as inoculators of other animals. 

In the case of the flea and plague, the insect 
is infective immediately or soon after it has in- 
gested blood, but the period of infectivity is lim- 
ited to a few days (Verjbitski) or at the most a 
few weeks (the Indian Plague Commission) . This 
has been referred to above as acute infection of 
the insect. Mechanical transmisssion is a term 
which has been used to signify the pure mechan- 
ical conveyance of micro-organisms by an insect 
from a diseased to a healthy animal. The role of periods of 
the flea in carrying plague may be simply a me- Infectlvlt >- 
chanical one, particularly when it transfers the 
disease immediately after its infection. But, inas- 
much as proliferation of the bacillus seems to 
occur in the flea, and since his infectivity may last 
for three weeks or more, proliferation may be re- 
sponsible for the later infectivity. In this event 
the transmission depends on biological as well as 



SO 1XFECTION AND IMMUNITY. 

and mechanical factors. Transmission of this type 
Transmission! probably demands a high degree of virulence and 
infectivity on the part of the micro-organisms, 
necessitating the introduction only of very small 
numbers. One of the conclusions of Verjbitski is 
that "animals could not be infected by the bites of 
fleas and bugs which had been infected by animals 
whose own infection had been occasioned by a cul- 
ture of small virulence, notwithstanding the fact 
that the insects may be found to contain abundant 
plague microbes." 10 

Another condition is represented in Rocky 
Mountain spotted fever, in which the insects are 
infective not only immediately or soon after suck- 
ing diseased blood, but also for an indefinite sub- 
sequent period. In this instance the tick under- 
goes generalized infection, as previously men- 
tioned. It is possible that the conveyance which 
takes place immediately after infection is of the 
mechanical type, but this cannot be true of the 
later transmissions, nor of those by the members 
of the following generation. In the latter we have 
to do with biological transmission, which in these 
two cases depends on proliferation of the micro- 
organisms and a general invasion of the tissues of 
the insects. The term '^biological transmission" 
was originally applied to those cases in which the 
micro-organisms (protozoan) undergo a compli- 
cated sexual cycle of development in the insect, as 
in malaria, but the principle remains the same 
with the bacterial diseases, although the method 
of proliferation is a simple one, consisting merely 
of fission. 

10. Jour. Hygiene, 1908, viii, 205. 



I3CUBATI0X IN IX SECTS. 81 

When the mosquitoes of malaria and yellow incubation 
fever suck diseased blood a definite incubation insects. 
period must elapse before they are able to convey 
infection to other individuals by their bites. Fol- 
lowing the ingestion of malarial blood by the mos- 
quito (various species of Anopheles), the parasite 
undergoes a sexual type of proliferation in the in- 
sect's stomach, the product of which, the sickle- 
shaped bodies, reach the salivary glands only after 
eight or ten days. These are the pathogenic forms 
of the parasite which are inoculated into man by 
the mosquito. In the intermediate stages of this 
cycle the parasite is not infective. The mosquito 
(Stegomyia) which transmits yellow fever is not 
infective until at least twelve days after it has 
sucked diseased blood. And it now appears also 
that a similar incubation period occurs in the 
tsetse fly in its role as the carrier of sleeping-sick- 
ness. After the insects are once infected, however, 
they continue virulent for a long time. Hence a 
primary non-infective stage is succeeded by a pro- 
longed infective stage in this type of transmission. 

On the basis of the conditions in malaria the 
temptation has been a strong one to conclude that 
a primary non-infective stage — incubation period 
— in the insect carrier is indicative of a sexual 
cycle in the development of the parasite; hence 
also of the protozoan character of the parasite. 
Thus it is anticipated in many quarters that the 
micro-organism of yellow fever, at present un- 
known, will prove to be a protozoan, because of 
the incubation period in the mosquito, mentioned 
above. Novy, however, has very aptly pointed out 
that an incubation period in the insect might well 
occur in the case of a bacterial disease as well as 



S2 INFECTION AND IMMUNITY. 

in a protozoon. 11 Given a case in which the dis- 

Transmission ease is caused by a bacterium rather than a proto- 

ac ena. zoon ^ We ma y assume? £ rs ^ that the infection in 

the insect is limited to its alimentary tract; or, 
second, that a generalized infection of the carrier 
takes place with a localization of the micro-organ- 
isms in its salivary glands. In the first instance 
a large proportion of the organisms ingested with 
the infected blood reach the stomach and intes- 
tines, whereas it is probable that a relatively small 
number remain in the proboscis. When the insect 
feeds at once, or soon, on another (healthy) ani- 
mal the number of micro-organisms injected from 
the proboscis may be insufficient to infect the new 
host. Some days might be required for prolifera- 
tion to result in an infective quantity, either in 
the proboscis, stomach, intestines, or by contiguous 
extension, in the salivary ducts and glands. At 
the time of inoculation the micro-organisms might 
simply be washed from the proboscis into the cutis 
by means of the salivary secretion, or directly in 
the latter, or after a certain amount of regurgita- 
tion from the stomach had taken place into the 
proboscis. 

In the second case, in which the insect under- 
goes a generalized infection, the primary non-in- 
fective period (incubation period) may well rep- 
resent the time required for this general invasion, 
with the consequent localization of the bacteria 
in the salivary glands. We have a very good 
analogy in typhoid fever in man, in which a very 
definite incubation period precedes generalized 
infection. 

11. The Role of Protozoa in Pathology; Proc. of the Path. 
Soc. of Philadelphia, 1907, pp. 1-27. 



Transmission. 



MODE OF INSECT TRANSMISSION. S3 

Hence it seems possible that errors may result 
in assuming that a primary non-infective period 
in the insect points, in an obligate manner, to the 
protozoan nature of a parasite. 

So far we have considered three types of trans- Types of 
mission by insects; the first, in which the insect is 
infective immediately or soon after ingesting dis- 
eased blood but not for a prolonged period (the 
flea in plague) ; the second, in which the carrier 
is infective almost immediately and for a prolonged 
period later (ticks in Eocky Mountain spotted 
fever) ; third, in which a harmless incubation 
period is followed by a prolonged virulent period 
(malaria and yellow fever). 

A fourth possibility, which is perhaps not yet 
thoroughly established, is that of an immediate 
infective period, followed by a non-infective, fol- 
lowed again by an infective. The conditions as as- 
certained so far indicate that this may be the case 
in the transmission of trypanosomes by tsetse flies. 
Until lately it was the experience that the flies 
could convey nagana only for one or two days 
after their feed on infected blood. Lately, how- 
ever, Ivleine 12 has found that an incubation period 
of about twenty days, or a little less, occurs in the 
fly, and from then on, even up to eighty-three 
days (Taute), it is able to transmit infection. 
This work has been done with the flies, Glossina 
morsitans and G. palpalis, in connection with the 
trypanosomes of nagana (T. brucei), and sleeping 
sickness (T. gambiense). The results have been 
corroborated by Bruce. The first stage of infec- 
tivity of the flies then remains for explanation. 

12. Deutsche med. Wchnschr., March 18, May 27 and July 
22, 1909. 



84 INFECTION AND IMMUNITY. 

It is possible that this is purely a mechanical trans- 
mission. In many of the experiments rather large 
numbers of flies have been used on a single animal, 
and in this case an infective quantity of the para- 
sites might well be introduced mechanically, where- 
as a single fly might be able to produce infection 
only after the parasite had multiplied in its tis- 
sues, and, perhaps, had reached the salivary glands. 
It is well known that an intermediate "insect 
stage" of the trypanosome is not required for infec- 
tivity, as appears to be the case with malaria. 
Trypanosomatic diseases may be carried directly 
from one animal to another by the injection of 
blood for an indefinite period. A sexual stage of 
the trypanosome has not yet been shown to occur 
in the tsetse fly. 
unique Type A unique type of insect transmission was de- 
TransmisTion. scribed recently by Miller 13 in the case of a dis- 
ease of rats which is caused by a protozoan organ- 
ism, Hepatozoon perniciosum, a new genus as well 
as a new species. The transmitter is a mite, 
Lelaps echidninus. The latter derives its infection 
by sucking the blood of diseased rats, in which the 
micro-organisms, at a particular stage of their 
development, occur within large mononuclear leu- 
cocytes. A sexual phase of the parasite takes place 
in the stomach of the mite, forming an ookinet. 
The latter penetrates the stomach wall, reaches the 
body cavity of the mite, and becomes encysted 
(oocyst stage). Within the cyst the parasite sub- 
divides to form a number of sporoblasts, each of 
which eventually contains from fourteen to twenty 
sporozoites. Miller readily produced the disease 

13. Bull. No. 46, Hygienic Laboratory, U. S. Public Health 
and Marine-Hospital Service, Washington, D. C. 



INSECT AND MULTICELLULAR PARASITES. 85 

in many rats by feeding them bread which had 
been mixed with crushed infected mites. The in- 
testinal juices of the rat break up the sporocyst. 
and set free the sporozoites, which as "vermicules" 
penetrate to the veins and lymphatics and reach 
the liver, where they undergo an asexual prolifera- 
tion within liver cells. From these the young 
merozoites are liberated and reach the general cir- 
culation, again as vermicules. It is the last stage 
which is taken up afresh by the mites. Although 
the sporocysts may occur in the salivary glands of 
the mite as well as in other parts of the body, Mil- 
ler found no reason to believe that the parasite is 
inoculated into the rat by the bite of the mite. 
The latter feeds only at night, leaving the host 
in the day, and at a subsequent feed may well 
reach a healthy rat, which in turn becomes in- 
fected b}^ eating a sufficient number of the mites. 
Miller reproduced the infection also by this "nat- 
ural" method. Other modes of infection, artificial 
in character, proved to be unsuccessful. 

That insects may have a relation to the main- insects and 
tenance and extension of some diseases caused by parasites™ 1 ** 1 * 
multicellular parasites is illustrated by the trop- 
ical and subtropical disease of filariasis, of which 
elephantiasis is one of the most pronounced clin- 
ical symptoms. The larval worms often exist in 
large numbers in the blood of man, particularly 
at night. When certain mosquitoes suck infected 
blood at this time one or more of the worms is 
ingested, undergo further development, and eventu- 
ally here through the stomach wall and reach the 
breast muscles of the insect. The exact manner 
in which the parasites are reinoculated into man 
is unknown. It was supposed by Manson that 



S6 INFECTION AND IMMUNITY. 

many of the female mosquitoes die in the water 
after they have laid their eggs and that the water 
thns becomes contaminated with the fllaria. The 
use of such water results in the infection of man 
through his intestinal tract. Suspicion falls on 
several species of mosquitoes : Culex pipiens, C. 
ciliaris, 0. faligans; Anopheles costalis, A. rossi, 
A. maculipennis. 

A number of worms which are parasitic in one 
animal or another are derived from insects, the 
latter serving as hosts for the larval stages. Infec- 
tion of the digestive canal originates after eating 
the insects (See Nuttall, Hygienische Eundschau. 
1899, ix, 505). 
specificity in There is a certain degree of specificity in the 
Transmission, transmission of a disease by an insect, but this is 
by no means absolute. In yellow fever it appears 
to be very strong, inasmuch as only one species of 
mosquito appears to be capable of cariying the 
disease (Stegomyia fasciata). An opposite ex- 
treme is found in the case of malaria, in which at 
least twenty-five different species of Anopheles 
have been shown to be capable of either natural or 
experimental transmission. 14 Several species of 
ticks are able to carry Texas fever and probably 
other piroplasmoses of cattle. At least two spe- 
cies of ticks carry Eocky Mountain spotted fever 
(Dermacentor venustus, Banks, and D. modestus. 
Banks). Two species of tsetse dies may carry the 
parasites of either nagana or sleeping-sickness. 
The carrying power, however, is usually limited 
to different species under a common genus. As far 
as observations have gone only Anopheles carry 

14 Ruge : Kolle and Wassermann's Handbuch d. path. 
Mikroorg. 



SPECIFICITY IN TRANSMISSION. 87 

malaria, only Glossina flies appear to transmit na- 
gana and sleeping sickness, and only Dermacentor 
ticks carry Eocky Mountain spotted fever. An 
exception is found to this in the case of a spiril- 
losis of fowls in South America. Naturally this 
disease is transmitted by a species of tick, Argas 
miniatus, but experimentally it may also be trans- 
mitted by Ornitliodorus moubata. The latter, in 
addition to transmitting the disease just men- 
tioned, may also carry the European relapsing 
fever, and is habitually concerned in the convey- 
ance of the South African tick fever of man. 



CHAPTER VII. 



SPECIAL FEATURES OF INFECTION. 

(1) Virulence, Toxicity, Etc. 

Patno- The word pathogenicity, in its relation to infec- 
vSruience! tion, refers to the power of an organism to produce 
disease, and often to the character of the changes 
which it causes. Virulence in all essential respects 
is synonymous with pathogenicity, but is used 
more commonly in describing the degree of path- 
ogenic power which a micro-organism posseses. 
Thus virulent and a virulent (or non- virulent) 
strains of the cholera vibrio or diphtheria bacillus 
are spoken of. 
Toxicity. Toxicity refers to" the poisonous properties of a 
microbe or its secretions. As a property it is not 
necessarily associated with the living micro-organ- 
isms. The question is still discussed as to whether 
toxicity and virulence are coextensive, even if they 
are not identical properties. Undoubtedly, toxicity 
is one of the factors on which virulence depends, 
and, from the standpoint of the micro-organism, it 
may be the sole property. Some organisms of little 
or no pathogenic or infective power nevertheless 
possess a protoplasm which is more or less poison- 
ous, as certain aspergilli, penicillia or Bacillus 
subtilis. 
infectivity. Infectivity, or infectiousness, relates to the 
power of a micro-organism to maintain itself and 
to multiply in a living host. One which is able to 



SPECIALIZATION IX VIRULENCE. 89 

obtain a foothold and to produce disease, even 
when a very minute quantity has been introduced ; 
or one which, after introduction, is able to prolifer- 
ate to an enormous degree in a particular host is 
said to be very infective, or infectious, for this host. 

Infectivity is not synonymous, nor is it neces- 
sarily coextensive, with virulence or pathogenicity. 
Thus Trypanosoma lewisi for the rat, the ma- 
larial parasites for the mosquito, and the virus of 
Rocky Mountain spotted fever for the tick are 
highly infective, but have a very low grade of path- 
ogenicity for these hosts. The leprosy bacillus, the 
spirochete of syphilis, and the tubercle bacillus 
have marked infectivity for man, but their viru- 
lence, as indicated by the slow progressive character 
of the diseases, may be considered as moderate, 
although the final event may be tragic enough. On 
the other hand, certain organisms possess great 
infectivity and great virulence at the same time, 
as plague, anthrax and the glanders bacilli (acute 
glanders) for man, and the trypanosomes of sleep- 
ing sickness, nagana and dourine for white mice. 

The virulence of some micro-organisms is often speciaiiza- 
specialized with regard to particular species of ani- violence. 
mals. Thus measles, scarlet fever and leprosy seem 
to attack man only, and no animal can be infected 
with their viruses. Smallpox and syphilis are less 
specialized. Smallpox can be inoculated into the 
ox and to a certain degree into the rabbit, and syph- 
ilis into monkeys, and perhaps also into the rabbit, 
although the latter may not yet be definitely deter- 
mined. Malaria and yellow fever infect only man 
and the mosquitoes which carry these diseases. 
Many other pathogenic organisms are in contrast to 
those mentioned, in that they are able to cause 



90 INFECTION AND IMMUNITY. 

disease in a wide range of animals. Such microbes 
are the pyogenic cocci, the bacilli of tuberculosis, 
glanders, typhoid fever, cholera, paratyphoid fever, 
tetanus, diphtheria, plague, certain of the trypano- 
somes, and many others. There are examples of 
immunity, however, even to these micro-organisms 
of rather general virulence, such as that of the alli- 
gator and the fowl to tetanus, and of the rat to 
diphtheria. 

In contrast to the examples mentioned above, 
are the non-pathogenic parasites, which experi- 
mentation has shown to have no, or insignificant 
virulence for any animal whatsoever. B. subtilis 
and B. megatherium are cited as representing such 
organisms. The former, however, is not absolutely 
without pathogenic power, since it has been observed 
as the cause of panophthalmitis in a number of 
cases, and by previously lowering intraperitoneal 
resistance (by the injection of "aggressins") Weil 
caused fatal peritonitis in guinea-pigs with this 
organism. 

Standing somewhat above these more or less 
harmless microbes in pathogenic power are the so- 
called acid-fast grass bacilli and similar organisms, 
which are able to produce only slight local changes 
in animals, and which are soon destroyed by the 
antibacterial agencies of the host. 
variations. Virulence is a variable factor even with regard 
to different strains of a given micro-organism. 
Diphtheria bacilli cultivated from various cases 
show a rather wide range of virulence, and similar 
observations have been made with regard to typhoid 
bacilli, streptococci, pneumococci, tubercle bacilli, 
plague bacilli and other organisms. With few ex- 
ceptions, pathogenic micro-organisms tend to lose 



PASSAGE THROUGH ANIMALS. 91 

virulence when they are cultivated for any length 
of time on the ordinary culture media. 

A common device for the maintenance or increase 
of virulence is that of passage through some suit- 
able animal. The process consists of the inocula- 
tion of the animal with a pure culture, permitting 
the infection to run its course or to proceed for a 
number of days, and at this time recovering the 
micro-organism on culture media from the tissues 
of the animal. Boux and Metchnikoff modified this 
technic by placing a culture of the organism in a 
sealed collodion sac, which is then imbedded in the 
peritoneal cavity of a living animal. After a suffi- 
cient length of time the sac is removed and the 
process repeated. By repeating the passage at suit- 
able intervals virulence may be maintained at a 
rather constant high point (cholera vibrio, strepto- 
cocci, etc.). An effective substitute for passage is 
sometimes found in the use of a culture medium, 
which in its constitution approximates that of the 
tissues of an animal. Thus the virulence of pneu- 
mococci and streptococci is retained by cultivation 
on blood agar or in rabbit or human serum or in 
ascitic fluid. 

Animal passage increases virulence in the most 
marked manner for the species of animal which is 
used in the experiment, although some increase is 
usually manifested toward other susceptible species. 
In a number of instances passage through one ani- 
mal results in a decrease of virulence for one 
species and an increase for another. Thus Pasteur 
found that passage of the virus of swine erysipelas 
(Schweinerotlauf) through pigeons increased 
virulence for the swine, but it was decreased for 
this animal when passed from rabbit to rabbit. 



92 INFECTION AND IMMUNITY. 

The virus of hydrophobia, when passed through 
several consecutive rabbits, and that of smallpox 
when passed through the calf, lose in virulence for 
man. 
Effect of The increase of virulence which results from 
passage has been explained by assuming that all 
the weaker and less virulent individuals of the 
culture are killed by the serum and leucocytes of 
the animal, leaving the more resistant and more 
virulent. This process of selection is probably an 
important factor in the change, but it would hardly 
explain the increase which occurs when an organism 
is grown on heated serum. It seems probable, as 
suggested by Eisenberg and others, that as a conse- 
quence of residence in the body of the animal the 
culture becomes immunized against the antibac- 
terial factors (bactericidal amboceptors and opson- 
ins) of the host, which would naturally render the 
organism a more dangerous one for subsequent 
animals into which it may be injected. It is even 
possible, as suggested by Welch and others, that 
certain elements in the body fluids may stimulate 
the micro-organisms to a more abundant secretion 
of toxins and other substances (amboceptors), and 
that the increased virulence caused by passage may 
• depend on the retention of this power after leaving 
the tissues of the host. 

It is probable that all organisms which are able 
to live for a shorter or longer time within the tis- 
sues of an animal cause anatomic changes and 
abnormal S}^mptoms sooner or later. This, of course, 
does not apply to those which live habitually on the 
cutaneous or mucous surfaces. Those which live 
on the skin do not reach the interior because of 
mechanical obstacles, and regarding those which 



DOSAGE OF MICRO-ORGANISMS. 93 

inhabit the mucous surfaces constantly, it would 
seem that an adaptation has taken place between 
such surfaces and the micro-organisms, so that the 
latter, although often pathogenic, are not able to 
reach deeper tissues. The least harmful infection 
of which one could conceive would be one in which 
the micro-organism disturbed the host in no way, 
except in so far as it used a certain amount of its 
substance for nutrition. This would be a case of 
simple, comparatively harmless, parasitism, which 
in man, is best illustrated by the organisms which 
live habitually on the mucous surfaces. 

It is possible that harmless tissue invasion finds 
examples in some of the insects, although this may 
not be maintained positively. The apparent harm- 
lessness of the organisms of malaria, yellow fever, 
South African tick fever and Eocky Mountain spot- 
ted fever for the insects which harbor them, was 
mentioned in the preceding chapter. Certain infec- 
tions do, indeed, run a very chronic and benign 
course, as the ordinary trypanosomiasis of rats, but 
they are not without discoverable, or even fatal, 
effects eventually. 

The quantity or dosage of micro-organisms re- 
quired for infection depends on their virulence 
and the degree of their parasitic power (infectiv- 
ity) ; this varies with different species and also 
with different strains of the same organism. The 
anthrax bacillus is very infective and may reach a 
high degree of virulence, so that a single organism 
has been known to produce fatal disease in experi- 
mental animals. Extremely minute quantities of 
some of the more virulent trypanosomes are 
required. The tubercle bacillus, even when most 
virulent, is hardly so infective ; it is said that eight 



94 INFECTION AND IMMUNITY. 

may produce infection when given intraperito- 
neally into the guinea-pig, and twenty to thirty 
when into the rabbit (Wyssokowicz). Many hun- 
dreds of the most virulent cholera vibrios and 
typhoid bacilli are required to produce fatal infec- 
tion in the guinea-pig. In contrast to the condi- 
tions mentioned are various saprophytic organisms 
which, regardless of the quantity introduced, either 
do not produce infection at all, or do so only after 
the resistance of the animal has been lowered arti- 
ficially. 

Among those who are equally exposed to infec- 
tion in an epidemic of typhoid fever, the escape of 
many probably is due to the ingestion of a small 
quantity of bacilli which is insufficient to produce 
disease. Individual susceptibility, and temporary 
low resistance, are other factors. 

(2) Types of Infection. 

There are wide variations in the physical rela- 
tionships which different pathogenic micro-organ- 
isms hold to the tissues of the body. This has 
already been suggested in the discussion of infec- 
tion atria, in which it was shown that certain 
organisms have a specific preference for points of 
primary invasion. 

This tendency of a specific relationship to par- 
ticular tissues is kept up in many instances after 
the microbes have reached the interior of the body. 

The malarial plasmodia enter and destroy the 
Bi\tributfoil! erythrocytes and cause enlargement of the spleen 
and liver, while other organs are affected to a 
much less degree as a rule. The pneumococcus 
has a great affinity for the pulmonary tissue and 
for endothelial structures; it frequently causes 



Selective 
Action and 



CUTANEOUS INFECTIONS. 95 

meningitis and is present in the blood in virtually 
all cases of pneumonia. The gonococcus, aside 
from its predilection for the urethra, readily 
becomes localized in the joints, and occasionally on 
the valves of the heart. The micro-organism which 
causes acute articular rheumatism has a specific 
affinity for the joints and endocardium. It would 
seem that the virus of hydrophobia attacks the cen- 
tral nervous system almost to the exclusion of 
other tissues. The spirochete of syphilis, although 
it may cause changes in any organ of the body, is 
particularly prone to produce proliferation of the 
vascular endothelium and subendothelial connect- 
ive tissue. 

The fungi which cause pityriasis versicolor, ^/^ction 8 
ringworm, barber's itch, erythrasma and favus 
attack only the cutaneous surfaces. Ringworm in 
the child is prone to be limited ta the scalp, whereas 
in the adult it occurs more commonly on the 
smooth skin. In ringworm and pityriasis versi- 
color only the superficial skin is involved, and in skin. 
the former the hair follicles and the hairs. In 
favus and barber's itch the cutis vera is often 
invaded, and in the former healing usually takes 
place with scar formation. The organisms appar- 
ently never become generally distributed in the 
body, and never, or rarely, cause symptoms of gen- 
eral intoxication. 

There are many other organisms of more general 
pathogenic powers which frequently cause infec- 
tions in the skin and other superficial tissues, 
although they have no specific relationship to the 
skin. They are found now in one tissue and now 
in another, and may in fact invade any organ of 
the body. Such organisms are the streptococci 



9G 



INFECTIOX AXD IMMUNITY. 



Intoxication 

Withonv 

Infection. 



(erysipelas), staphylococci (acne, furunculosis), 
the bacillus of anthrax (malignant carbuncle), the 
tubercle bacillus (lupus, anatomic tubercle), blasto- 
mycetes, and others. It is a rather peculiar 
feature of tuberculosis and blastomycosis that, 
given a primary infection of the skin, there is not 
a marked disposition to the metastatic invasion of 
deeper and remote tissues. "This does occur occa- 
sionally, it is true, but it seems that a primary 
localization in the skin has a tendency to immunize 
the rest of the body against invasion by these 
organisms. 

Diphtheria and tetanus, as stated elsewhere, rep- 
resent another type of local infection, the former 
involving mucous surfaces, the latter being a wound 
infection. In these, the organisms do not become 
generally distributed in the body, or, at any rate, 
not to a marked and essential degree, but the gen- 
eral intoxication results from the action of specific 
soluble toxins which are absorbed and distributed 
through the body by the circulation. The organ- 
isms are largely limited to the point of primary 
invasion or implantation. Their toxins may be 
obtained free from the bacterial cells in artificial 
culture media, and such toxins when injected are 
able to cause the symptoms of the disease. 

The bacillus of botulism belongs to the same 
group as the tetanus and diphtheria bacillus, in 
that it produces a specific soluble toxin in culture 
media which is able to cause the symptoms of the 
disease. The mechanism of pathogenesis is differ- 
ent, however. The toxin which produces the dis- 
ease has already been formed in the diseased meat 
by the bacillus before the meat is eaten, and the 
poisoning results from the absorption of this toxin 



CONTINUOUS INVASION. 97 

through the wall of the intestines. The bacillus 
itself is believed not to proliferate in the intes- 
tines. The condition is one of intoxication with- 
out true infection. 

In some of the intestinal diseases the cavity of continuous 

J Invasion 

the intestines appears to act as a sort of reservoir from » 
in which the organisms proliferate to an unlimited 
degree, and from which they reach the circulation 
more or less continuously in large numbers, either 
in a living or dead condition. This relates particu- 
larly to typhoid, paratyphoid, cholera and dysen- 
tery. They are primarily surface infections. In 
the two former, however, the organisms, during 
the early days of infection, reach the circulation in 
a living condition in large numbers, and may even 
proliferate in this situation. In cholera, the vibrios 
show a disposition to general invasion, but appear 
to be killed off before they have actually pene- 
trated the intestinal wall. The same condition 
probably prevails in bacillary dysentery. It is the 
general belief that the intoxication in these 
instances comes about through the disintegration 
of the micro-organisms, as a consequence of which 
a poisonous protoplasm is set free. This conception 
has its origin from the facts that it has been diffi- 
cult or impossible to obtain potent soluble toxins 
in culture media, and that the bodies of the killed 
organisms are sufficiently toxic to explain the 
intoxication. Eecent work, however, indicates that 
a certain quantity of toxin may be produced in arti- 
ficial cultivation, and it is possible that the condi- 
tions in the body are much more favorable for CUronic 
toxin production than are artificial surroundings, j 10 ?** 1 }?^ 

Certain chronic infections, even when they involve without 
deeper tissues and internal organs, show from the Extension. 



98 INFECTION AND IMMUNITY. 

start a disposition to remain localized, although in 
the end they may involve various organs, by means 
of metastases, and in some of them a more or less 
continuous blood infection may arise. Such dis- 
eases are tuberculosis, actinomycosis, blastomyco- 
sis (oidiomycosis), rhinoscleroma, sporotrichosis, 
and perhaps leprosy. They are characterized by 
the formation of a good deal of fibrous tissue, 
which tends to limit rapid extension by the forma- 
tion of metastases, and by a disposition to invade 
contiguous tissues. New foci may be set up in 
distant organs by means of metastasis, the blood- 
stream in the meantime being comparatively free 
from living micro-organisms. A true septicemic 
condition may be produced,, in tuberculosis by the 
sudden pouring of large quantities of bacilli into 
the circulation from a cheesy focus which has 
ruptured into a vessel. This again results in the 
formation of many minute foci in various parts 
of the body (diffuse miliary tuberculosis). The 
conditions are similar in blastomycosis, leprosy 
and glanders. Barely metastatic infection with 
actinonTyces is found. 

These chronic infections are not the only ones, 
however, in which new foci may originate by 
metastasis. A streptococcus infection of the heart 
valves, or an infected thrombus in some vein, cause 
"pyemic" abscesses in various organs when infected 
clots from the original site are set free in the circu- 
lation. The foci of infection found in the kidney in 
typhoid fever, and the involvement of the joints 
in gonorrhea, are further examples of metastatic 
invasion. 
secondary As already indicated, systemic infection may 
infections, take place in a secondary and accidental way in 



SYSTEMIC INFECTIONS. 



many cases when a pre-existing local disease exists 
at some point. In a small group of diseases 
(typhoid, paratyphoid, pneumonia) this second- 
ary general invasion occurs with great constancy, 
and the organisms can always be cultivated from 
the blood if this is undertaken at the proper time. 
In syphilis general invasion occurs only after a 
certain "incubation period" has been passed in 
the primary sore, and after this time it exists as a 
protracted blood infection. 

Others appear to be primarily and essentially 
blood infections, little or no reaction taking place 
at the point of invasion. This is true of systemic 
plague, anthrax, Rocky Mountain spotted fever, 
some very virulent infections with the streptococ- 
cus, relapsing fever, and in many of the protozoan 
infections, as in malaria, piroplasmosis, and in 
sleeping sickness. In some of these the organisms 
may pass a portion of the incubation period 
in the lymph glands, where they proliferate 
to such an extent that they gradually over- 
whelm the circulation in large numbers. The 
organisms of malaria and piroplasmosis proliferate 
in the blood-stream, i. e., within the erythrocytes. 
It also seems probable that the other organisms 
mentioned are able to proliferate in the plasma, 
and that their presence in the blood-stream is not 
due entirely to their continuous escape from such 
solid organs as the lymph glands and spleen, or 
from the point of primary invasion. They are true 
or full parasites in the sense of Bail. 

From the standpoint of continuity there are sev- 
eral types of systemic infection. 

We may, in the first place, recognize the continu- 
ous type, in which the organisms, after they once 



Primary 
Systemic 
Infections. 



Continuous 

Systemic 

Infections. 






100 INFECTION AND IMMUNITY. 

reach the circulation, persist in that situation until 
the infection terminates either in death or recovery, 
in the latter case being exterminated by the pro- 
tective agencies of the blood. Typhoid and para- 
typhoid fever, plague, Eocky Mountain spotted 
fever, Malta fever, and probably the acute exanthe- 
mata, are of this type. Eecovery and the steriliza- 
tion of the blood, however, does not mean that the 
whole body is necessarily rid of the micro-organ- 
isms; the latter still may persist for a greater or 
less period on one or more of the body surfaces, as 
in the case of typhoid fever, in which the bacilli 
may persist in the intestines or the bladder for a 
long period, or in plague in which the organisms 
may be found in the sputum for some time. 
Through some accident typhoid may vary from its 
usual habit, a point which is illustrated by the 
occasional occurrence of relapses, or by the locali- 
zation of the bacilli in some solid organ of the 
body, as in the vertebrae or the muscles, resulting 
in post-typhoidal complications. 
Periodic ^ n other instances the systemic invasion is of 
infection^ periodic character, and of this there are a number 
of varieties. The streptococcus, when it exists as 
the cause of fibrinous endocarditis or of thrombo- 
phlebitis, often invades the circulation in a fluctu- 
ating manner. Periods when there are very few 
cocci in the blood will be followed by others in 
which they are very numerous, and the clinical 
symptoms usually correspond with these fluctua- 
tions. A similar course probably is followed by 
tuberculosis and blastomycosis in their invasion of 
the blood. Mechanical factors sometimes precipi- 
tate a systemic distribution, such as the rupture of 
a caseous nodule into a vessel or lymph channel in 



RECRUDESCENCES IN INFECTIONS. 



Regular 
Recurrences. 






tuberculosis, or the separation of minute fragments 
of thrombus infected with streptococci. 

Examples of a more or less regular periodicity 
are found in the various relapsing fevers, which 
are caused by spirilla. The first attack of the 
European relapsing fever lasts for six or seven 
days. This is followed by a period of apyrexia of 
five or six days, followed by another febrile period. 
Eecovery is usually established after three or four 
such attacks. In the relapsing fever of South 
Africa the first attack has a shorter duration 
(about three days), and those which succeed may 
last only one or two days, according to Koch. 
During the febrile attacks the blood swarms with 
spirilla, whereas in the intervals it is compara- 
tively free from organisms. In explanation of this 
it has been assumed that the febrile attacks are cut 
short by the development of a certain degree of 
immunity. This results in a more or less complete 
sterilization of the blood, although spirilla which 
remain in the lymphoid organs, particularly the 
spleen, seem to be protected. At the time of a 
relapse, either the immunity has decreased suffi- 
cient^ or the remaining organisms have gained in 
virulence to such an extent that a general reinva- 
sion takes place. In the end the immune forces 
gain the upper hand and the body becomes com- 
pletely sterilized. 

Some of the chronic infections are subject to Recmdes- 

CCI1C6S in 

irregular recrudescences. Syphilis and trypanoso- syphilis, etc, 

miasis of man begin as acute infections. After 
the acute secondary stage has apparently passed, 
syphilitics frequently surfer recrudescences, with 
general manifestations, and it is probable that the 
number of micro-organisms in the blood increases 



102 



INFECTION AND IMMUNITY. 



Cyclic 

Invasion in 

Malaria. 



at such times. In the first stage of sleeping sick- 
ness, the so-called trypanosomatic fever, the fever 
is of a remittent type, and during the attacks of 
fever the number of trypanosomes in the blood 
increases. In the stage of sleeping sickness they 
appear to be limited very largely to the lymphatic 
glands and the meninges. They can readily be 
obtained from these sites by puncture, but their 
presence in the blood is much more inconstant. It 
has been the experience that on some days pro- 
longed examination of the blood will disclose no 
trypanosomes ; on other days two or three per field 
may be found ; and on still others as many as seven 
or eight per field. 

The tertian and quartan infections with the 
malarial parasites, at least in their early stages, 
illustrate a special type of recurrent generalized 
infection, which is cyclic in nature, the period of 
intense general invasion coinciding with a certain 
stage of the asexual multiplication of the parasites. 
(See chapter on malaria.) 

(3) Nature and Mechanism of Infection. 

penetration by -^ * s t° be understood that infection presupposes 
Micro- a penetration of the body surfaces to a greater or 

organisms. " . . . . 

less degree. Even in pityriasis versicolor, the 
most superficial of infections, the fungus pene- 
trates the horny layer of the skin. Hence, in a 
consideration of the nature and mechanism of 
infection, it would be desirable, first of all, to con- 
sider the manner in which micro-organisms and 
their poisons may reach the deeper tissues. In 
some instances this is readily understood, whereas 
in many others we must in the main be content 
with mere deductions. 



ABSORPTION OF TOXINS. 103 

Certain animal parasites, as the itch mite and Skin. 
jigger, penetrate the surface through mechanical 
defects of their own making. 

In penetrating wounds, abrasions and transmis- Mechanical 

1 . ° , „ . Implantation. 

sion by insects the introduction of micro-organisms 
is a question of mechanical inoculation, or subse- 
quent growth into the defect. In this case there is 
no barrier to their entrance into the circulation, 
until after the appearance of an inflammatory 
reaction; and if the organism happens to be one 
which secretes a soluble and easily diffusible toxin 
(e. g., tetanus bacillus), general intoxication may 
result even without further dissemination of the 
living cells. The degree of defect necessary for 
infection varies with the character and virulence of 
the organism. The bacilli of plague, anthrax, 
glanders, and the spirochete of syphilis may enter 
through lesions which are almost microscopic in 
size. These organisms possess great infectivity, 
exceedingly small numbers producing infection. 

Organisms, such as virulent staphylococci, which penetration by 
reach the hair follicles and sebaceous glands, are G?o^-tu.° us 
able to grow through the succulent epithelium into 
the surrounding tissues, and to cause a furuncle, 
carbuncle or cellulitis. This may follow or be 
accompanied by a primary necrosis of the epi- 
thelium. Occasionally when furuncles are situated 
at favorable spots, as near the angle of the mouth 
or nose, the necrosis may extend to adjacent veins, 
resulting in a flooding of the circulation with the 
organisms. 

True soluble toxins are seldom absorbed through 
the unbroken skin, if we except the case of poison- 
ing with poison ivy. In Moro's test for tuberculo- 
sis the tuberculin, incorporated in a paste, is 



INFECTION AND IMMUNITY. 



Mncous 
Surfaces. 



Contiguous 
Growth. 



rubbed into the skin. This is also true of most 
chemical poisons which do not have a corrosive 
effect, although by prolonged contact (lead) or 
rubbing (mercury) a certain amount of absorp- 
tion may be induced. 

In infections of the mucous membranes, with 
their soft epithelial covering and moist surfaces, 
micro-organisms are often able to grow through 
into the underlying tissue, resulting in either a 
local inflammation, a general infection through 
the medium of the lymphatics or capillaries, or a 
general intoxication through the absorption of 
toxins. A mechanical defect in the surface may 
not be necessary for this penetration, the exten- 
sion taking place by contiguous growth, which, 
however, is surely favored by any toxic and desqua- 
mating effect which the organism or its toxin may 
have on the epithelium. Streptococci which reach 
the crypts of the tonsils readily cause necrosis of 
the surface epithelium, and this defect would seem 
to facilitate deeper invasion. 
Diphtheria. The growth of the diphtheria bacillus is limited 
in the main to the superficial layers of the tissues 
which it attacks. As the organism penetrates the 
epithelial layer, possibly by direct growth, the toxin 
which it secretes causes necrosis of the adjacent 
cells. This process continues until the vascular 
tissues are reached, resulting in the formation of a 
false membrane. However, the onset of fever 
before the formation of the membrane, and the 
occurrence of diphtheria without membrane forma- 
tion, show that the false membrane, i. e., the necro- 
sis of the surface, is by no means a prerequisite for 
the absorption of the toxin. A severe invasion of 
the body by the bacillus does not occur, although 



as Carriers. 



LEUCOCYTES AS CARRIERS. 105 

occasional individuals, without doubt, reach the cir- 
culation; this, however, is not necessary for the 
general intoxication. 

Leucocytes are continuously passing from the Leucocytes 
tonsils, intestines and other superficial organs 
which are rich in lymphatics, through the mucous 
membrane to the surface. These excreted leuco- 
cytes may often be seen engorged with large num- 
bers of bacteria which they encounter on the sur- 
face, and it has been suggested that the excreted 
leucocytes may re-enter the adjacent tissue, carry- 
ing bacteria with them. The study of sections of 
the intestines, tonsils and peribronchial lymph 
glands has shown that bacteria are continuously 
entering the body, even in health, and their fre- 
quent occurrence within leucocytes which are near 
the surface suggests that the latter are the agents 
through which they are introduced (Kuffer, Biz- 
zozero and others). This finding, however, could 
not be accepted as proof of the hypothesis, since 
the phagocytosis may have taken place after the 
organisms had penetrated the surface independ- 
ently. 

Through the work of Nocard, Bavenel, Behring 
and others, it has been shown that tubercle bacilli 
will pass into the lymphatics from the intestines, 
in the absence of mechanical defects. 

That the leucocytes may perform this function 
is also suggested by A. B. Macallum's study of the 
absorption of iron. When the albuminate and pep- 
tonate of iron were fed to starved lizards, the min- 
eral, eight hours later, was demonstrated in large 
quantities in the leucocytes contained in the lumen 
of the intestines, also within leucocytes which lay 
between the epithelial cells of the villi (re-entering 



INFECTION AND IMMUNITY. 



Denudation 
of Surface. 



leucocytes ( ! ) ,and within similar cells which were 
found in the liver and spleen (Adami's Principles 
of Pathology, Vol. I, p. 291). Inasmuch as no 
power of spontaneous penetration can be ascribed 
to the particles of iron, it is held that they were 
carried into the tissues by inwandering leucocytes. 

It may be stated, then, as a reasonable probabil- 
ity that micro-organisms are sometimes carried into 
the deeper tissues by leucocytes which re-enter the 
surface. 

Phagocytosis of bacteria by epithelial cells, par- 
ticularly by the pulmonary epithelium, is known to 
occur, but it is not known that the process is an 
essential one for invasion. 

Some toxins are not readily absorbed by the nor- 
mal mucous membranes, whereas others seem to be 
taken up readily. In the absence of wounds, tet- 
anus toxin, when ingested, causes no symptoms. 
It is destroyed largely by the gastric and pan- 
creatic juices, and this is the case also with diph- 
theria toxin in test-tube experiments. The latter 
has the power of causing necrosis of the mucosa, 
and may be absorbed through the injured surface. 
The toxin of hay fever is readily absorbed through 
the conjunctiva and the mucous membrane of the 
nose. Experimentally, ricin, a plant toxin, is 
absorbed through the intestines, although the 
amount required for fatal intoxication by this 
route greatly exceeds that of the subcutaneous 
injection. The toxin of the bacillus of botulism 
is readily absorbed through the intestines of both 
man and animals. 

When a micro-organism causes a primary des- 
quamation of the mucous epithelium, it follows 
that further penetration of the organism, as well 



IXCUBATIOy PERIOD. 



107 



as absorption of toxins, are facilitated. This would 
seem to find special application in cholera and 
bacillary dysentery. In cholera general invasion 
of the body by the living organisms does not take 
place, although the intestinal surface is denuded 
to a greater or less degree. The vibrios penetrate 
to a certain rather superficial depth, where they 
appear to become dissolved, and with their dissolu- 
tion, poisons, in addition to those which were pre- 
viously secreted, are set free. The conditions are 
similar in dysentery. 

To summarize, micro-organisms gain entrance to summary, 
the subjacent tissues through wounds, by means of 
their own power of injuring the surface and grow- 
ing into and through it, and probably also through 
the agency of inwandering leucocytes. Phagocytic 
epithelial cells in some instances may play a part, 
but this is hypothetical. Toxins are absorbed for 
the most part through surfaces which have been 
previously injured, but some of them are able to 
pass through previously healthy mucous mem- 
branes. 

The term incubation period signifies the inter- 
val between the first introduction of a pathogenic 
micro-organism, or its toxin, until the develop- 
ment of the first symptoms which characterize the 
onset of the disease. In many infections, as in 
typhoid fever, a feeling of malaise, headache and 
nausea, frequently appear a few days before marked 
symptoms develop, and this period is called the 
prodromal stage. It may be considered either as 
the latter end of the incubation period, or as the 
beginning of actual "onset." 

The length of the incubation period varies Duration 
greatly in different infections. In cholera it may 



Incubation 
Period. 



108 INFECTION AND IMMUNITY. 

be as short as a few hours only, in hydrophobia it 
is on rare occasions as long as six months, but 
more commonly two to four weeks. In a rather 
large group of diseases the onset follows in from 
one to two weeks after exposure, so that there 
would seem to be a tendency to some general law, 
the basis of which is not known. 

It has been suggested that it may have a relation 
to the anaphylactic reaction (Eosenau and Ander- 
son) ; namely, that the first micro-organisms intro- 
duced "sensitize" the body in some way not yet 
understood, and when sensitization has taken place 
(seven to fourteen days) the body then has a 
greater susceptibility to the organism and yields 
readily to infection (see "Anaphylaxis"). 

Occasional individuals show a susceptibility to a 
first injection of horse serum (e. g., diphtheria 
antitoxin) in that they develop an urticarial rash, 
adenopathy, effusions into the joints, and perhaps 
fever, in from eight to twelve days after the intro- 
duction of the serum. Von Pirquet noted that 
when a second injection of the serum was given 
after an interval of two weeks or more similar 
symptoms would develop within a few hours rather 
than after several days; and there is a great deal 
of constancy in this when susceptible individuals 
are concerned. He arrived at the conclusion that the 
horse serum as such is not toxic for man, but that 
as a consequence of the injection antibodies to the 
serum are formed and that the intoxication comes 
about as a result of some kind of chemical reaction 
which takes place between the antibodies and the 
serum. The conditions in immunization render 
this explanation extremely probable. After the 
first injection of serum antibodies to the serum 



INCUBATION AXD DOSAGE. 109 

(precipitating and perhaps other antibodies) are 
found in considerable concentration in the blood 
only after the lapse of some daj^s. If the injection 
of serum given in the first place was of some size, 
some of the original serum proteids would still be 
present in the body when the antibody formation 
had reached a high point, and the conditions for 
the toxicogenic reaction between the two would be 
present. This would account for the delayed reac- 
tion seen in first injections. If some smaller quan- 
tity were given in the first place the delayed reac- 
tion might not occur, because the serum proteids 
would all have been modified or excreted. If a 
second injection is given, however, the fresh serum 
at once comes in contact with the antibodies which 
have already been formed, and the toxic combina- 
tion or substance can be produced at once. 

On the basis of these considerations von Pirquet 
believes that the ordinary interpretations of the 
nature of the incubation period are incorrect. 
As he says : "I presented the theory that the dis- 
ease-producing agent only calls forth pathological 
symptoms in the body when it is changed b}' means 
of the antibodies; the incubation period is the 
period required for the formation of these anti- 
bodies." This possibility cannot be overlooked 
in a present-day consideration of this subject, 
although it is still on a theoretical foundation. 

The number of micro-organisms introduced has 
an influence on the incubation period. Guinea- 
pigs may be killed within a few hours by the injec- 
tion of a large quantity of typhoid bacilli, but with Relation 
the administration of smaller quantities a much 
longer incubation period may be obtained. The 
effect of quantity also is shown very clearly by the 



of Dosage. 



110 



INFECTION AND IMMUNITY. 



injection of diphtheria or tetanns toxins, by which 
the incubation period can be shortened from sev- 
eral days down to several hours, depending on the 
quantity injected. 

The so-called true toxins of bacteria, i. e., those 
which are able to cause the formation of antitoxins, 
as a rule are distinguished from other poisonous 
substances of bacterial or other origin, by the occur- 
rence of an incubation period when they are admin- 
istered. However, at least two toxins, venom and 
that secreted by the Vibrio Nasih and perhaps 
other vibros, act so quickly that an incubation 
period is hardly to be recognized. 

The number of micro-organisms originally enter- 
ing the body is usually quite small; hence the time 
required for them to reach an infective or toxic 
quantity probably represents a part of the incuba- 
tion period. 

In hydrophobia and tetanus a mechanical fac- 
tor plays a part in the length of this stage. In 
these cases the micro-organisms (hydrophobia) and 
toxin (tetanus) appear to reach the central nerv- 
ous system by way of the peripheral nerves, and 
symptoms are delayed until this occurs. Wounds 
of the face and neck are followed by symptoms 
more quickly than when they are situated on parts 
more remote from the central nervous system. 
Adaptation. It is not unlikely that another factor consists of 
a certain relation between the protective powers of 
the host and the invasive or aggressive ability of 
the organism, at least in some instances. Lemaire 
and also Buxton found that after the injection of 
pathogenic micro-organisms directly into the cir- 
culation, there is at first a reduction in their num- 
ber, followed by reneAved proliferation, which 



Proliferation. 



Mechanical 
Factors. 



Resistance.' 



SERUM RESISTANCE OF ORGANISMS. Ill 

progresses steadily. Supposedly, the natural anti- 
bacterial forces of the serum and leucocytes took 
up the destruction of the bacteria uutil the former 
were exhausted, and from this time proliferation 
could take place with little hindrance. In infec- 
tions which occur naturally, as in typhoid fever or 
scarlet fever, the first organisms which reach the 
underlying tissues and circulation may be 
destroyed, involving such a loss of bactericidal 
agencies that continued proliferation and invasion 
finally results in general infection. 

In speaking of passage, it has already been ^serum 
stated that virulence may be increased by permit- 
ting an organism to grow in the tissues of a living 
animal. Virulent organisms are not taken up by 
leucocytes so readily as avirulent, and in the pres- 
ence of high virulence there may be no phagocytosis 
at all. This has a bearing on the incubation period 
in that the micro-organisms which first come in 
contact with the tissues of the host may have low 
virulence, but after exposure to the germicidal 
substances for a sufficient length of time, their 
pathogenicity and resistance may be so raised that 
they escape destruction in the tissues. On this 
basis, therefore, the incubation period may, in part, 
represent the time required for the organisms to 
become serum-resistant. 

Eegarding the subject under discussion, there is 
still another factor which finds application, par- 
ticularly where toxins having an enzyme-like 
nature, are involved. Toxins have been likened to 
enzymes, because of their action in exceedingly 
small doses, their common susceptibility to heat, 
and finally the exhibition of an incubation period. 
"No matter how much diphtheria or tetanus toxin 



112 INFECTION AND IMMUNITY. 

is introduced into an animal, the incubation period 
cannot be eliminated absolutely; and some of the 
hemolytic toxins, as tetanolysin, can be added to 
red blood cells in test-tubes in any desired quan- 
tity without causing their immediate solution. 
There is, therefore, something inherent in the 
nature of these substances, or in the nature of the 
action which they exert on the cells of the body, 
which demands this latent period before an effect 
becomes manifest. 

It seems probable, therefore, that there are many 
factors which contribute to the existence of the 
incubation period, and that the factors which 
determine its length in one instance may not be 
identical with those which are found in another. 
The time required for proliferation of the micro- ■ 
organism to an infective quantity probably is com- 
mon to all infections. The infective quantity must 
vary with different diseases, and with different 
strains of the same micro-organism depending on 
their virulence. A virulent strain has a shorter 
incubation period than a less virulent. In some 
instances a certain amount of time may be 
required for the micro-organism to undergo an 
increase in virulence sufficient to accomplish infec- 
tion. Or, again, this time may be required for the 
exhaustion (absorption or chemical binding) of 
the protective substances to such a degree that fur- 
ther proliferation and invasion take place with 
greater rapidity, this latter step coinciding with 
the onset of marked symptoms. The time required 
for distribution of the poisons to vital organs would 
seem to be of minor importance except in hydro- 
phobia and tetanus, which utilize the peripheral 
nerves as a route to the central nervous system. 



AFFINITIES OF TOXIN 8. 



Establish- 
ment of 
Infection. 



Direct 

Chemical 

Injuries. 



In the case of some of the toxins (as of diphtheria 
and tetanus) a certain time for the manifestation 
of a toxic effect is required, even when they are 
placed in direct contact with the cells for which 
they have a specific affinity. x\s stated, the role of 
anaphylaxis is uncertain. 

Leaving out of consideration the few instances Factor: 
in which preformed toxins are ingested and 
absorbed (as in botulism), the production of dis- 
ease in a susceptible host would seem to depend on 
two factors : First, presence in the micro-organism, 
or secretion by it, of a toxin which is able to cause 
a direct injury of the tissues of the host; and sec- 
ond, ability of the micro-organism to remain alive 
and to proliferate in the body of the host. 

Different toxins vary greatly in the cells which 
they attack. Some destroy the red blood cells to a 
marked degree (staphylococcus and streptococcus) ; 
others have a special affinity for the nervous tissue 
(tetanus, diphtheria, botulism) ; some attack par- 
ticularly the endothelium of the vessels, causing 
many minute hemorrhages (some of the eruptive 
fevers, rattlesnake venom). In many other in- 
stances the toxins have a wider range of action, 
and many different tissues suffer to a greater or 
less degree. Areas of necrosis in the lymphoid and 
parenchymatous organs, and granular and fatty 
degeneration of the latter, and of the muscles, 
including the heart, are well known in different 
diseases. The albumin and casts which appear in 
the urine in various acute febrile diseases are a 
result of a toxic action on the epithelium and endo- 
thelium of the kidneys. 

In addition to destroying life by their direct 
action on the cells, pathogenic micro-organisms 



IXFECTWX AXD IMMUNITY. 



Mechanical 
Injuries. 



Connective 
Tissue. 



produce profound disturbances in metabolism and 
nutrition by interference with the functions of 
organs. It is not the intention, however, to enter 
into a discussion of these obscure influences. 

The mechanical injuries which micro-organisms 
cause are, at least in most cases, the result of a 
previous toxic action, i. e., they are secondary 
effects. This is true of the emboli, consisting of a 
mixture of fibrin, cells and micro-organisms, which 
arise in a valvular endocarditis, and of thrombi 
which are formed in vessels as a consequence of 
infection. 

In lobar pneumonia we have a good example of a 
mechanical disturbance of importance. The alveoli 
become filled with a fibrinous and purulent exudate 
which makes a large area of pulmonary tissue 
unavailable for respiration. Yet, even here, the 
mechanical disturbance has arisen only as a result 
of the toxic action of the pneumococcus on the 
capillary walls and the alveolar epithelium, per- 
mitting the escape of the blood and serum. 

Some chronic infections are characterized by the 
development of new connective tissue and vessels; 
this is seen especially in syphilis, tuberculosis and 
actinomycosis. The import of the new connective 
tissue depends on its location. A large amount of 
it may form in pre-existing fibrous tissues with no 
consequent harm; but even a small scar, gumma 
or tubercle in the brain, or deformities of the heart 
valves which follow inflammation, may cause 
serious results. 

A genuine direct mechanical disturbance appears 
to be caused by the malarial organisms in that 
they occasionally accumulate in the capillaries of 
the intestines and brain in such numbers as to 



RESISTANCE OF ORGANISMS. 



amount to virtual thrombosis. Filarial, which are 
multicellular organisms, cause grave conditions by 
occlusion of the lymphatics. 

In discussing the second condition for the occur- 
rence of infection, namely, the ability of the 
micro-organism to remain alive and to proliferate 
in the body of the host, this must be done with 
regard to certain protective agencies which the host 
possesses against invading micro-organisms. 

As will appear later in more detail, these agencies Anti- 
may be directed either against the toxins of the a nd Antitoxic 
micro-organisms, or against the parasitic cells Aseiicies - 
themselves. The former rests in the antitoxins 
which may be present in the plasma and lymph, 
and the power of the tissues to bind and destroy 
the toxins ; the latter in the germicidal substances 
of the body fluids (the so-called bacteriolysins), 
and in the phagocytic and destructive action of 
various cells of the bod} 7 , particularly the leucocytes 
and endothelial cells. Manifestly, in actual infec- 
tion the micro-organisms are able to proliferate in 
spite of the presence of these antagonistic agencies, 
and the conditions which render this possible prob- 
ably vary a great deal in different infections. 

Thus, in relation to tuberculosis, either the Natural . 

7 . . . n Resistance of 

serum of man and animals possesses no germicidal organisms. 
substances for this particular organism, or the lat- 
ter is resistant to their action. Also, since the 
bacilli are frequently found within phagocytic 
cells in a good state of preservation, it would 
seem that they have a certain degree of resistance 
to intracellular digestion. Staphylococci, strepto- 
cocci and certain other organisms resist destruction 
by the serum, although they are readily taken up 
and destroyed by phagocytes. 



116 INFECTION AND IMMUNITY. 

Acquired This insusceptibility of the tubercle bacillus and 
^oiganisms! the cocc i mentioned to the germicidal action of 
the serum is a natural and constant property. On 
the other hand, certain organisms which are nat- 
urally susceptible to the germicidal power of the 
serum and leucocytes appear to acquire a resistance 
against these agencies during the course of infec- 
tion, and it is not at all unlikely that this is a 
property which is common to all pathogenic micro- 
organisms. We may look on this change as a 
phenomenon of adaptation. In a distinct sense it 
appears that the micro-organisms may become 
immunized to the bactericidal substances of the 
serum, and to the opsonins on which destruction 
by phagocytosis depends. 

The increase of virulence in a micro-organism 
by repeated passage through a suitable animal may 
be regarded as an adaptation on the part of the 
organism for the tissues and fluids of the animal, 
and in this adaptation an increased resistance to 
the germicidal substances probably is an important 
factor. Similar agencies doubtless are at work in 
the maintenance of virulence by growing cultures 
on media which contain the serum of animals. 

Typhoid bacilli which have been cultivated from 
the body of a patient recently are more resistant 
to agglutination than those which have been on 
artificial media for some time. The same has been 
found true of the cholera vibrio (Pfeiffer and 
Kolle), as well as of some other organisms. Also 
the cultivation of bacteria (typhoid bacilli) in 
media which contain an agglutinating serum brings 
about an increased resistance to agglutination 
(Eansom and Kitashima, Walker, Steinhardt and 
others) ; and it has been shown that such modified 



Resistance to 
Agglutinins. 



BA CTERI0LYS1 JS. 1 1 7 

bacilli absorb or bind less agglutinin than "nor- 
mal" strains (Miiller, Cole, Eisenberg). Explained 
in terms of Ehrlich's theory, it is assumed that 
they contain a decreased number of binding 
molecules or receptors for the agglutinin, hence an 
effective quantity of the latter is not bound. 

Experiments by many observers indicate that 
bacteria may also acquire resistance to the bac- iysins. 
tericidal action of the serum, and that this prop- 
erty goes hand in hand, at least to a certain extent, 
with the virulence of the micro-organism. In some 
of these experiments the resistance has been 
acquired by growing the organisms in the corre- 
sponding antiserum, for a greater or less length 
of time. Thus Cohn, by growing the typhoid 
bacillus on antityphoid serum, conferred on it an 
increased resistance to bacteriolysis, which was 
retained for several subsequent generations on agar. 
Day also, in a similar way, caused increased serum 
resistance in B. prodigiosus, B. vulgaris and B. 
fluorescens, and even conferred some pathogenic 
powers on these organisms, which naturally are 
rather harmless saprophytes. 1 Such results have 
been obtained with the organisms of typhoid 
(Walker, Haffkine and others), cholera (Szekely, 
Ransom, Kitashima and others), dysentery (Mar- 
shall, Knox, Mason), anthrax (Shaw, Danyz and 
others), the colon bacillus (Hamburger), Vibrio 
metchnikovi (Metchnikoff, Bordet and others). It 
has frequently been found also that bacteria when 
freshly cultivated from infections have an 
unusually high resistance to the bactericidal action 
of serums. Besserer and Jaffe noted that a strain 

1. Eisenberg gives a summary of this and kindred subjects 
in the Centralbl. f. Bakteriol., etc., xlv, No. 2. 



Resistance to 
Bacterio- 



118 INFECTION AND IMMUNITY. 

of the typhoid bacillus isolated from a "carrier" 
may show this increased resistance. 
Resistance to It is an old tenet of Metchnikoff that virulent 

Phagocytosis. 

micro-organisms are less susceptible to phagocyto- 
sis than avirulent. This was supposed to be due 
to the establishment of a negative chemotaxis, 
which consisted either in a repelling of the leuco- 
cytes or in their failure to be attracted to the bac- 
teria. In 1892 Massart reported that leucocytes 
were negative chemotactically to virulent strains of 
the organisms of anthrax, chicken cholera, swine 
plague, and to B. pyocyaneus and Vibrio metchni- 
kovij and that they were taken up by leucocytes in 
the animal experiment to a much less extent than 
avirulent strains of the same organisms. The same 
condition was noted in relation to staphylococci 
(van der Velde, Kocher, Taval). Since phagocy- 
tosis has been studied more extensively under arti- 
ficial conditions, the same phenomenon has been 
noted in relation to other organisms, as the strepto- 
coccus (Hektoen and Euediger, Bordet, etc.), 
pneumococcus (Eosenow), typhoid and paraty- 
phoid bacilli (Neufeld and Hiine, Hektoen), the 
colon bacillus (Beattie), the meningococcus (Flex- 
ner), and others. In African tick fever, Levaditi 
and Roche noted the presence of spirillicidal and 
opsonic substances (those favoring phagocytosis) 
following the first attack of fever, but they 
appeared to be effective only on the spirilla which 
were present in the blood during the first attack. 
By the time the second attack occurred the organ- 
isms had acquired a resistance to these substances 
which they retained during several passages 
through rats subsequently. It would seem that 
this acquired resistance on the part of the organ- 



RESISTANCE TO DRUGS. 119 

isms is what makes the second attack possible, and 
that this might go indefinitely were it not that the 
host eventually responds by the production of 
such a quantity of germicidal substances that the 
spirilla are finally destroyed. We may suppose 
that the conditions are not very different in syph- 
ilis and in some of the chronic protozoic infections, 
as trypanosomiasis and piroplasmosis ; in all these 
diseases specific antibodies are produced during the 
course of infection, and there is good reason to 
believe that some of these are germicidal in charac- 
ter. This is certainly true in regard to piroplasmo- 
sis and trypanosomiasis, yet the organisms persist 
in the blood and tissues of the host for a long 
period. It seems that they must have become 
adapted to the presence of these germicidal sub- 
stances. That virulence is not lost as a consequence 
of this adaptation is shown by the fact that the 
blood when it is injected into a fresh animal repro- 
duces a typical acute attack. 

It is noteworthy that a similar resistance to cer- Acquired 
tain drugs can be induced in trypanosomes when Jcf Drugs! e 
infected animals are given repeated injections of 
these preparatoins. If a sufficient quantity of one 
of these drugs (atoxyl, fuchsin, trypan-red, etc.) 
is given to an infected animal, a complete cure, 
with sterilization of the body, may be obtained. In 
the event, however, that an insufficient quantity 
of the drug is administered, the organisms when 
injected into a subsequent animal may be entirely 
indifferent to the presence of the drug, which, con- 
sequently, has lost its therapeutic value against 
this strain. It may be necessary to repeat this 
process through many passages before a high degree 
of drug resistance is obtained, but when once estab- 



120 



INFECTION AND IMMUNITY. 



Capsule 

Formation. 



Injury of 

Protective 

Agencies. 



lished it is of long duration. Such strains are 
called "chemoresistant." It has also been shown 
that trypanosomes acquire a resistance to the 
germicidal properties of serum, as in the case of 
bacteria. 

In view of the fact that some micro-organisms 
produce a capsule when grown in the animal body, 
whereas it is absent in ordinary culture media, it 
has been supposed by some that the capsule is an 
expression of adaptation on the part of the organ- 
ism to the germicidal agencies of the host, that it 
is perhaps protective in its character. Such 
observations have been made in relation to the 
anthrax bacillus (Deutsch and others), the strep- 
tococcus (Bordet, Marchand and others), and the 
plague bacillus (Lohlein). 2 This relationship, how- 
ever, is not general, and can hardly be considered 
as thoroughly established. 

In addition to this more or less passive adapta- 
tion on the part of micro-organisms, there is rea- 
son to believe that they may actually antagonize 
the protective agencies of the body, particularly 
the process of phagocytosis. Arloing and Cour- 
mont, and Roger believed that bacteria secrete sub- 
stances which favor their growth in the body. 
Roger observed that an extract of the bacillus of 
symptomatic anthrax when injected into the rabbit 
favored infection with this organism. Bouchard 
spoke of such elements as substances favorisantes. 
Kruse (Zeiglers Beiirage, xii, 339) also believed 
that such substances exist and called them collect- 
ively lytische Sustanzen, Angriffstoffe, oder Lysine. 
He supposed that their effect was chiefly to neu- 
tralize the alexins, the name which, at that time, 



2. Cited by Eisenberg, 1. c. 



LEUC0CID1X. 121 

was applied to the bactericidal substances of the 
serum. Their existence had no satisfactory sup- 
port at that time. 

A little later van der Velde discovered that Leucccidin. 
staphylococci secrete a substance which is toxic for 
leucocytes, the so-called leucocidin. It appeared to 
be produced by strains of both high and low viru- 
lence. Still more recently it was discovered that 
the streptococcus produces a toxin which is 
destructive for leucocytes (Ruediger, Besredka). 
These results suggest that a toxic action on the 
leucocytes may be a factor for the progress of 
infection, and may explain, at least in part, the 
resistance which virulent organisms show toward 
phagocytosis. A particularly significant observa- 
tion is that by Eosenow, to the effect that virulent 
pneumococci secrete a substance which has the 
power of inhibiting phagocytosis, a substance to 
which the name of virulin was given. Virulin can viruiin. 
be extracted from virulent cultures by means of 
salt solution, and after this has taken place the 
cocci have become susceptible to phagocytosis. Also 
after avirulent strains have been treated with the 
extracted virulin, and later separated from it by 
washing, they are found to have acquired resist- 
ance to phagocytosis. Eisenberg also observed that 
leucotoxic substances are produced by the bacilli of 
symptomatic anthrax and malignant edema. He 
furthermore believes that it is a more or less com- 
mon property of bacteria to produce such sub- 
stances in the course of infection, although they 
may not be obtained under artificial conditions, 
and that they are identical with the "aggressins" 
of Bail. The correctness of this belief, however. 
is not fully demonstrated. 



122 INFECTION AXD IMMUNITY. 

As'sressins. Bail, discrediting the importance of the germi- 
cidal substances of the serum for natural immun- 
ity, assigns to phagocytosis the essential role, and 
believes that the virulence of the parasites depends 
on their power to produce substances, the aggres- 
sins, which antagonize the process of phagoc}^tosis. 
The aggressins were supposed to be non-toxic sub- 
stances which were produced only in the body of 
the infected animal. When the organisms of 
typhoid, cholera, tuberculosis and other diseases, 
are injected intraperitoneally into the guinea-pig, 
the aggressins appear in the inflammatory exudate, 
and are obtained free from living micro-organisms 
by centrifugation and subsequent chemical sterili- 
zation of the overlying fluid. This fluid, when 
mixed with the homologous culture, has the power 
of rendering fatal a quantity of the culture which 
otherwise would be unable to produce infection, 
and the mixture may cause a very acute death of 
the experiment animal. Bail found all the more 
justification for assuming the existence of this new 
( ?) substance from the fact that immunization 
with the aggressins gives rise to a serum which 
has the power of neutralizing the effect of the 
aggressive exudate; hence such a serum was termed 
an antiaggressin. 

objections. The studies of others, however (Wassermann and 
Citron, Doerr, Sauerbeck and others) indicate that 
the aggressins of Bail do not represent a new entity. 
Wassermann and Citron found that the "aggres- 
sins" as prepared by Bail are toxic, and that they 
may be obtained in artificial cultures as well as in 
the body of an animal. They probably represent 
nothing more than the cytoplasm of dissolved bac- 
teria which may exert an inhibiting effect on pha- 



ADAPTATION OF ORGANISMS. 123 

gocytosis in more than one way. The toxic 
substances may injure the leucocytes to such an 
extent that they do not readily take up the living 
organisms; since they represent disintegrated 
organisms, they may, like the latter, absorb or 
"bind" the opsonins of the plasma, on which 
phagocytosis depends, and thus prevent the action 
of the opsonins on the bacterial cells; similarly, 
they bind the bacteriolysins of the serum, and 
hence divert their action from the living cells; 
also, since the dissolved organisms are toxic, when 
the "aggressins" are added to living cultures, the 
total toxicity for the animal is increased by just 
that much. There is also evidence to show that the 
most indifferent proteid substances when injected 
into an animal may decrease its resistance to infec- 
tion or intoxication for the moment. Thus Kick 
etts and Kirk found that a small quantity of egg 
albumin, broth, or normal serums (goat, guinea- 
pig) when injected into white mice, decrease the 
resistance of the latter to a concomitant inocula- 
tion with tetanus toxin. The foreign substances 
were supposed to pre-engage the absorptive and 
digestive powers of various cells (leucocytes, etc.), 
so that the toxin was disposed of less readily, and 
more remained available for the highly susceptible 
nervous tissues. 

The remarks just made are not intended to cast 
doubt on the probability that pathogenic micro- 
organisms produce substances which are antago- 
nistic to phagocytosis. That the latter action 
really occurs has already been indicated. 

In previous paragraphs attention was called to Response ana 
the fact that micro-organisms attempt to adapt the^ost? 11 
themselves to their hosts, to the end that the latter 



124 INFECTION AND IMMUNITY. 

may be a more favorable medium for their exist- 
ence. Thus, they increase in virulence, and disarm 
the host by becoming resistant to its protective 
agencies, and even actively antagonize the latter, 
particularly as regards phagocytosis, and by such 
means the natural immunity of the host is rendered 
inefficient. The host, however, is not without its 
own reserve forces, and, in favorable cases, after 
infection is once established, it responds to the pres- 
ence of the micro-organisms by the production of 
a new supply of protective "antibodies," the effect 
of which is to destroy larger numbers of the invad- 
ing organisms, or even to sterilize the body com- 
pletely. In the latter case recovery is the prob- 
able event. This, again, may be looked on as a 
process of adaptation on the part of the host, in 
which it seeks to destroy or render less noxious the 
infecting microbes. 
Mutual In certain chronic infections it seems that a 

Adaptation. 

mutual adaptation takes place, so that there is a 
tendency for the host and parasite to live in a half- 
way state of harmony. Thus, in the acute stage 
of syphilis, the "combat" between the host and the 
spirochetes is an active one. Eventually, however, 
it would seem that the host reacts by the produc- 
tion of protective antibodies, a condition which 
results in an amelioration of the symptoms. Since 
the micro-organisms may remain alive and viru- 
lent in the host for a long time after this has 
occurred, it appears that they become habituated 
to the presence of the antibodies, while the host 
at the same time becomes habituated to the toxicity 
of the spirochetes. After the lapse of still further 
time the adaptation on the part of the patient 
appears to increase, and the micro-organism also 



1 M M UXIZIX G BE8P0 y SE. 



125 



loses in virulence, if we may judge from the low 
infectivity usually accredited to tertiary lesions, 
in spite of the fact that they contain the spiro- 
chetes. This mutual adaptation, however, does not 
mean that the host escapes injury as a consequence 
of the infection. Similar conditions probably pre- 
vail in piroplasmosis and trypanosomiasis, or even 
in relapsing fever, as suggested previously. 

What has come to be known as the hypothesis of Hypothesis 
Welch may be mentioned in this connection. It 
may be put in the form of the following question : 
If bacterial toxins and the constituents of bacterial 
cells so act on the tissue cells that the latter pro- 
duce bodies (antibodies) which are inimical to the 
bacteria, why may not the body fluids in turn so 
act on the bacteria that the latter produce bodies 
(antibodies) which are inimical to the tissue cells? 
"Looked at from the point of view of the bac- 
terium, as well as from that of the animal host, 
according to the hypothesis advanced, the struggle 
between the bacteria and the body cells in infec- 
tions may be conceived as an immunizing contest 
in which each participant is stimulated by its 
opponent to the production of cytotoxins hostile 
to the other, and thereby endeavors to make itself 
immune against its antagonist" (Welch). 

That bacteria may acquire increased resistance 
to the destructive agencies of the host was referred 
to above; but the hypothesis of Welch means a 
great deal more than the immunization of the bac- 
teria against the defensive powers of the animal 
body. Not only may a bacterium during an infec- 
tion become more resistant to the bactericidal 
action of the body by producing antibodies to those 
bactericidal agencies, or by its ability to absorb 



Immunizing 
Response by 
Micro- 
organisms. 



126 INFECTION AND IMMUNITY. 

and dispose of a greater quantity of bacteriolysiu 
or opsonin; and not only may a bacterium be able 
to respond to the presence of natural antitoxins in 
the body by the production of more toxin, the 
occurrence of which under artificial conditions was 
shown by Wechsberg in relation to the diphtheria 
bacillus; but, in addition, certain constituents of 
our body fluids may, by combining with suitable 
bacterial receptors, stimulate the bacterium to the 
production of a whole shower of cytotoxins, which 
attack the leucocytes, erythrocytes, nerve cells, 
liver, kidney, etc. The nature of the animal sub- 
stances which may combine with the bacterial 
receptors and thus cause the formation of the bac- 
teriogenic cytotoxins is left an open question and 
is not of essential importance to the theory; it is 
not at all necessary that they be toxic to the bac- 
terium, and they may even be taken up as food 
substances. Likewise the possible nature of the 
cytotoxins produced by the bacterium is of second- 
ary importance. It so happened that Welch 
assumed that they might be of the nature of ambo- 
ceptors which may be complemented by bacterial 
complement, by the circulating complement of the 
body or by endocomplements of the tissue cells. 
One could with equal reasonableness assume that 
they may be complete toxins, receptors of the sec- 
ond order, with a haptophorous and a toxophorous 
structure. 

In some support of this general lrypothesis is the 
observation that the strongest leucocidin (a toxin 
for leucocytes) can be obtained from the staphylo- 
coccus by inoculating this organism into a serous 
cavity of animals, the toxin being obtained subse- 
quently from the mixture of cocci and leucocytes. 



ATREPTIC IMMUNITY. 127 

Investigations have not advanced far toward the 
positive determination of the correctness of the 
hypothesis. 

In Ehrlich's conception of "atreptic" immunity, 
the possibility is entertained that micro-organisms 
sometimes may not be able to grow in a host 
because the nutritive conditions are not suitable. 
It probably would be granted that proper nutritive 
substances are present in the host, but it is assumed 
that they may be so intimately and firmly bound 
to other tissue constituents that they are not avail- 
able to the micro-organisms as food. Virulent 
micro-organisms find the nutritive substances 
already available, or, if this is not the condition, 
the injury which they effect on the tissues in the 
first instance results in a splitting of the con- 
stituents so that the food substance (rather a spe- 
cific food substance) becomes available. Avirulent 
organisms not having the power to produce this 
splitting result do not proliferate to any great 
degree and soon become the prey of the protective 
agencies, such as the leucocytes and bacteriolysins. 
With this theory in mind, one recurs to the 
"exhaustion 77 theory^ of immunity at one time 
entertained by Pasteur, and cited in a previous 
chapter. This difference appears, however, that in 
Pasteur's theory an entire absence of suitable food 
was assumed, whereas in the atreptic theory the 
food substance may be present but not available for 
the use of the organisms. The atreptic theory is 
put forward as being a possible factor in resistance 
to some infections by some hosts, not, of course, as 
a theory intended to supplant other general 
theories of immunit}^. 



PART TWO 



CHAPTER VIII. 



TYPES OF IMMUNITY. 

By immunity we understand that condition in 
which an individual or a species of animal exhib- 
its unusual or complete resistance to an infection 
for which other individuals or other species show 
a greater or less degree of susceptibility. Immune 
is from the Latin immunis, which originally ap- 
plied to one who was exempt from a public service, 
exempt from tribute, or free. Although the word 
retained this civil meaning for centuries, and still 
retains it in certain connections, it also had, even 
in ancient times, a limited application to the pro- 
tection which an individual might possess against 
poisons. It is seen, for example, in descriptions 
of a tribe inhabiting Northern Africa, the Psylli, 
who were said to possess a natural immunity to the 
bites of poisonous snakes. Although we may be 
certain from this and other references that a con- 
dition of immunity was recognized in very ancient 
times, the present significance of the term has 
developed largely from a better understanding of 
the nature of infectious diseases and of the condi- 
tions upon which the resistance of the body de- 
pends. 

As the definition suggests, we do not think of 

'"immunity, immunity to such processes as Bright's disease, 

arteriosclerosis or the metabolic diseases, but only 



Concerned in 



NATURAL IMMUNITY. 129 

to those which we have learned to recognize as 
infectious. The fact that an individual is free 
from gout, diabetes or any other metabolic disturb- 
ance, cannot be taken as indicating an immunity 
from these diseases. Inasmuch as the metabolic 
diseases appear to depend on the failure of certain 
organs to perform their functions normally, for 
some one or more reasons, we can only infer that 
in those who are free from such diseases the corre- 
sponding organs are in a state of normal activity. 
Similarly an individual or race which is free from 
an infectious disease because of lack of opportun- 
ity to contract it would not be classed as immune. 

Immunity has no necessary relationship to the 
degree of contagiousness of an infectious disease, 
although some of the most striking and certainly 
the most common examples of immunity are seen 
in relation to such infections (as scarlet fever and 
smallpox). Tetanus, on the other hand, which is 
absolutely non-contagious, can likewise give rise 
to a high degree of immunity. 

No medical fact is more widely known among Acanired 
intelligent people than that an attack of certain immunity. 
of our infectious diseases brings about some kind 
of change in the patient's tissues which protects 
him, or renders him immune, against further at- 
tacks of the same disease. Inasmuch as he was 
previously susceptible, the new property is an ac- 
quired one, and he is now said to possess an ac- 
quired immunity against this infection. 

It is also well known that many diseases which Natural 
attack man can not be inoculated into animals, Immunlt y« 
and biologists are familiar with many examples 
of immunity which are confined to particular spe- 
cies. The lower animals apparently can not be in- 



Immunity. 



130 INFECTION AND IMMUNITY. 

fected with scarlet fever or measles, nor man with 
chicken cholera. The negro is less susceptible 
than the white man to yellow fever. The resist- 
ance which these examples illustrate exists natur- 
ally, not through having the disease ; it is a natural 
immunity. 
Family Sns- Natural immunity is, for the most part, an in- 
and herited condition; this certainly is the case where 
a whole class of animals is involved. Similarly, 
the susceptibility which is peculiar to a species 
must be hereditary. It is often said of some dis- 
eases that they "run in families ;" e. g., carcinoma, 
gout, insanity. This appears to be just as true of 
some infectious diseases, the most noteworthy ex- 
ample of which is probably tuberculosis. In con- 
trast to this inherited susceptibility is an inherited 
immunity, which may also "run in families." It -is 
not so easy to adduce examples of this. We are in 
the habit of thinking of the individual who can 
resist all infections as representing a standard. 
He, however, is above the average in resistance, 
and the average is our proper standard for esti- 
mating the resistance of a species or race of ani- 
mals. It is undoubtedly true that some families 
possess an unusual resistance to tuberculosis. 
Furthermore, experimental work with animals has 
proved that, within limits, an immunity to cer- 
tain infections (e. g., tetanus) acquired by a fe- 
male may be transmitted to her offspring. Such 
immunity, however, is very transient in character, 
and is "passive" in its type; it depends on the 
transfer of protective substances from the circula- 
tion of the female parent to that of the embryo 
in utero, and some weeks after the birth of the lat- 
ter these substances are eliminated and the immun- 



ceptibility. 



ACQUIRED SUSCEPTIBILITY. 131 

ity disappears. That of the parent, however, per- 
sists for a much longer period; it is "active" in 
character, as explained later. Even in a given 
la.rn.ily, however, there are often marked variations 
in susceptibility and resistance. One child in a 
family may contract scarlet fever, while another, 
living under exactly the same conditions, may 
escape it. 

Susceptibility also is often acquired in a more 
or less evanescent way. The resistance of an indi- 
vidual may vary greatly at different times and 
under different conditions. These are accidental, 
acquired states such as may be occasioned by 
exhaustion, hunger, exposure to cold and other 
unhygienic conditions. 

Eecently, the existence of a specific acquired Acquired sn 
susceptibility to various proteid substances and 
bacterial products has been determined by experi- 
mentation. An injection of serum or various pro- 
teicls into the proper animal renders it extremely 
susceptible to a second injection; and a person 
who is suffering from a particular infection shows 
unusual sensitiveness to the products of the organ- 
ism causing the infection, as shown by the tuber- 
culin reaction of Koch. Such animals and indi- 
viduals are said to have been sensitized. This sub- 
ject will be discussed later under "Anaphylaxis." 

Many of these facts were familiar long before 
anything was known regarding the principles on 
which they depend. Subsequent to the discovery 
of some of these principles (to be considered 
later), it became convenient and necessary to rec- 
ognize other special types of immunity, although 
any type which can be conceived must still find a 
place under either natural or acquired immunity. 



132 



INFECTION AND IMMUNITY. 



Antibacterial 

Immunity. 






Phagocytosis. 



Although such diseases as typhoid and cholera 
are accompanied by pronounced toxic symptoms, 
the poisonous substances seem to be integrally as- 
sociated with the bacterial protoplasm and not 
secreted in a soluble or diffusible form by the liv- 
ing cell ; they are spoken of as intracellular toxins 
or endotoxins. Observations point to the belief 
that the endotoxins are liberated only after the 
bacteria are killed and dissolved. When one, 
through infection, has acquired immunity to ty- 
phoid or cholera, his fresh serum is able to kill the 
respective bacterium, but apparently is not able to 
neutralize its toxic substance. Hence, on the basis 
of the nature of the serum, immunity to such dis- 
eases is spoken of as antibacterial rather than 
antitoxic. 

Although the subject is still in a developmental 
state, the conditions indicate that there are two 
factors in antibacterial immunity, one in which 
the plasma or serum has a marked power of kill- 
ing the micro-organisms, the other in which the 
destruction is largely by means of phagocytic cells. 
The former was just referred to. Both agencies 
operate in many infections, as in typhoid, cholera 
and others; whereas in other instances (strepto- 
cocci, staphylococci) phagocytosis is the only de- 
tectable protective agency. In most cases phago- 
cytosis cannot take place until certain constituents 
(opsonins) in the plasma or serum have "sensi- 
tized" the bacteria. In case of recovery the power 
of phagocytic destruction is usually enhanced. We 
have, therefore, to recognize phagocytic immunity 
as a type, or at least as an important factor, in 
both n itural and acquired resistance. 






ANTITOXIC IMMUNITY. 133 

In contrast to infections of the type referred to 
above are others in which the symptoms are pro- 
duced by soluble toxins, the ectotoxins, which are 
secreted by the micro-organisms. 

The symptoms which are so characteristic of ^muSty. 
tetanus are produced, not by contact of the bacteria 
with the nervons system, but rather through the 
specific soluble toxin which is secreted by the bacilli 
in the wound where they reside. This poison, or 
toxin, is carried from the wound to the nervous 
system through the lymphatic or blood circulation, 
the bacterium itself not being transported. There- 
fore, although tetanus is a bacterial disease, it is 
at the same time and in a peculiar sense a toxic 
disease. The serum of an animal which has 
acquired immunity to diphtheria or tetanus neu- 
tralizes the corresponding soluble toxin, but does 
not necessarily injure the micro-organism itself. 
That is to say, the immunity is antitoxic. 

Experience has shown that this distinction 
between antibacterial and antitoxic immunity is 
an important one, and the differentiation is very 
sharp in some instances, particularly in acquired 
immunity. In many examples of natural immun- 
ity, the resistance cannot be attributed so specific- 
ally to antibacterial or antitoxic serum properties. 
This is referred to later. 

In the types of immunity referred to, the fac- 
tors on which the resistance appears to depend, 
i. e., the germicidal or antitoxic action of the 
serum or the germicidal power of the leucocytes, 
are susceptible to experimental demonstration. We 
are familiar with another type of resistance, how- 
ever, which finds no expression in the form of 
antitoxins or other antibodies. This relates par- 



134 



INFECTION AND IMMUNITY. 



Active 

Immunity. 



Immunity. 



ticularly to habituation to various drugs, as mor- 
phin, cocain or arsenic, to which a high resistance 
may be acquired. The true explanation of such 
resistance is not known, but it would appear to 
depend on some acquired property by the cells 
which were originally more susceptible; in other 
words, it would appear to be an immunity which 
is fixed in the cells, a static immunity, so to say, 
if the expression may be coined. It may depend on 
habituation alone, on an increased power of de- 
stroying the poison by the cells, or on a decreased 
affinity of the cells for the poison. 

A similar process may exist in acquired resist- 
ance to some of the more chronic infections, as 
tuberculosis, leprosy and others, although very lit- 
tle is known definitely concerning it. 

Immunity which results from an infection de- 
pends on a specific reaction on the part of the 
tissue cells in response to the chemical injury pro- 
duced by the bacteria or their toxins. The indica- 
tions of the occurrence of such a reaction lie, first, 
in the recovery of the patient, and, second, in the 
new antitoxic or antibacterial power which may be 
demonstrated in the serum or the increased phago- 
cytic power of his leucocytes. In view of the active 
part played by the body in establishing this new 
resistance, the condition is referred to as an active 
immunity. In the preparation of various anti- 
toxic and antibacterial serums for therapeutic pur- 
poses, a condition of active immunity is deliberate- 
ly produced in the animals (the horse, for exam- 
ple) by the injection of the toxins or of the bac- 
teria. 

Contrariwise, the resistance which is established 
in an individual through the injection of an im- 



TYPES OF IMMUNITY. 



135 



mime serum (such as diphtheria antitoxin) is a 
passive immunity, since it depends on the intro- 
duction of ready-made immunizing substances 
rather than on their production through an active 
process on the part of the one injected. Active 
and passive immunity, then, are varieties of ac- 
quired immunity. Depending on the disease 
which caused the immunity, or on the character 
of the serum injected, they may be antibacterial 
or antitoxic, or, to a certain extent, opsonic (pha- 
. gocytic) . 

Any one of the types mentioned may be either 
relative (partial) or absolute (complete). If the 
immunity is absolute, infection is impossible. If 
only relative, different conditions may be made 
to prevail which would render infection possible; 
for example, a large number of bacteria will often 
cause an infection where a smaller number fails 
to do so. There may also be a temporary decrease 
in one's resistance through overwork, hunger or ex- 
posure. Immunity is usually relative. 

By proper combinations of the terms which 
have been enumerated, one may describe somewhat 
accurately the different forms of immunity. Thus, 
a child which has received a prophylactic injec- 
tion of diphtheria antitoxin is in a state of ac- 
quired passive antitoxic immunity to diphtheria. 
If immunity to typhoid has developed as a result 
of the disease, the condition is that of an acquired 
active antibacterial immunity, etc. Accordingly, 
although the terms may be somewhat confusing, 
it is seen that they are in no sense contradictory. 

The following classification of the agencies which 
may contribute to immunity in one disease or 
another may be given, although we must recognize 



Relative and 
Absolute 

Immunity. 



Classification 
of Types. 



136 INFECTION AND IMMUNITY. 

that it probably does not include all conceivable 
factors. 

FACTORS IN IMMUNITY. 
Natural Immunity : 

1. Antibacterial properties of the serum or plasma. 

2. Antibacterial properties of the leucocytes in cooperation 

with opsonins (preparers for phagocytosis). 

3. Antitoxic properties of the serum or plasma, resulting 

in a simple binding or neutralization of toxins. 
Hypothetically, too, certain ferments of the body 
may split or decompose toxins. 

4. Total insusceptibility of the body to endotoxins or exo- 

toxins. There is reason to believe also that com- 
parative resistance sometimes depends on the fact 
that a toxin has a stronger affinity for organs of less 
vital importance for the life of the individual than it 
has for more important organs. The chicken, for 
example, is very resistant to tetanus, although its 
serum contains no antitoxin. It yields, however, 
when inoculations are made directly into the nervous 
tissue. 

5. The "atreptic"' immunity of Ehrlich, in which micro- 

organisms do not find suitable food, or food in avail- 
able form, in the body of the host. This is theoreti- 
cal at present. 

Acquired Immunity : 

1. Increased antibacterial properties of the serum or 

plasma. 

2. Increased phagocytic power of the leucocytes, and per- 

haps other phagocytic cells, depending on the increased 
formation of opsonins. 

3. Increased antitoxic properties of the serum or plasma. 

4. Habituation of the cells to bacterial poisons. 

Under 3 and 4, we may have also to consider an 
increased power of splitting or digesting toxic sub- 
stances. Of this, however, we know nothing defi- 
nite. 

One and 3 (possibly also 2) may be passive as 
well as active. These subjects receive further con- 
sideration in subsequent chapters. 



CHAPTEE IX. 



NATURAL IMMUNITY. 

Natural immunity to infection depends, first, on 
certain obstacles to invasion which are afforded 
by the body surfaces and the germicidal effect of 
their secretions; and, second, on antibacterial and 
antitoxic forces which are present in the cells and 
fluids of the interior body. 

(1) Protection Afforded by the Body Surfaces 

Virulent organisms (e. g., staphylococci and Tlie skin. 

streptococci) exist normally on the skin or be- 
tween the superficial horny cells, some exceptional 
circumstance being necessary, e. g., wounds, to en- 
able them to penetrate deeper and to cause disease. 
It is evident, then, that the physiologic shedding 
of the superficial horny cells and their continual 
reformation at a deeper level is a process calcu- 
lated to rid the surface of the body of many micro- 
organisms. 

The question whether micro-organisms can ever 
penetrate the unbroken skin has been much dis- 
cussed. Although experiments have shown that 
traumatism is not absolutely necessary, clinical 
experience indicates that these so-called crypto- 
genetic infections are not of ready occurrence. 
When they do occur, the infection atrium is prob- 
ably one of the glandular orifices. 

The sweat glands with their ducts, and the hair Cutaneous 
follicles with their appended sebaceous glands, 






13S INFECTION AND IMMUNITY. 

are vulnerable points in the defense which the 
cutaneous surface represents. Although they are 
protected somewhat by the flow of their excretions, 
especially in warm weather, and although the en- 
trance of germs is made more difficult by the con- 
traction of the skin and consequent narrowing of 
the orifices in cold weather, yet various incidents 
may lead to the introduction and retention of 
virulent micro-organisms in these structures. 
When this occurs there is little difficulty in the 
way of their producing necrosis of the epithelium, 
invading the surrounding tissue and causing a 
pustule, boil, carbuncle, cellulitis, or even a gen- 
eralized infection. The secretion of the sebaceous 
glands appears to be not germicidal. On the other 
hand, the acid nature and certain salts found in 
perspiration render this fluid antagonistic to the 
development and virulence of certain micro-organ- 
isms. 

The serous exudate, and the crust which forms 
subsequent to an abrasion, antagonize infection. 
The serum itself contains germicidal substances, 
while the crust mechanically prevents microbic 
invasion. 
^co^nectivl Soluble poisons such as aconite and bacterial 
Tissue, toxins are not absorbed through the unbroken skin. 

Even after germs penetrate the epidermis, the 
subcutaneous connective tissue is often an obstacle 
to their further extension. The subcutaneous in- 
jection of some micro-organisms (e. g., cholera) 
is tolerated better by animals than one given into 
the abdominal cavity or blood vessels. We are 
also familiar with the benign course of lupus 
compared with visceral tuberculosis; the same is 
true of cutaneous and visceral glanders. This re- 



JIUCO US MEM BR AXES. 



139 



Mucous 

Membranes. 



distance is explainable, at least in part, by the 
rapidity with which new connective tissue forms 
in the subcutaneous tissue, offering a mechanical 
limitation to the infection, and by the rich lymph 
supply which makes possible the rapid accumula- 
tion of bactericidal lymph and of phagocytic cells. 
On the other hand, it must be mentioned that in 
some diseases the subcutaneous tissue offers no 
perceptible resistance to bacterial invasion 
(plague), and that toxins may be more virulent 
when introduced into this tissue than when in- 
jected into the abdominal cavity or the general 
circulation (tetanus). 

The moist condition of mucous membranes has 
been found to favor the multiplication of many 
microbes, although mucus itself is said to atten- 
uate the virulence of some micro-organisms, as 
the pneumococcus ; mucus, however, is not actively 
germicidal. A layer of mucus, on the other hand, 
is a mechanical protection, and its constant excre- 
tion is a means of- steadily removing bacteria from 
mucous surfaces. 

The conjunctiva is protected against infection conjunctiva. 
by the mechanical interference of the eyebrows, 
eyelashes, eyelids, irrigation of the conjunctival 
surface by tears which carry germs through the 
lachrymal duct into the nasal cavity, the ability 
of the conjunctival epithelium to repair itself 
rapidly, and the mild germicidal action of the 
salts which are present in the tears. These pro- 
tective agencies, however, are often surmounted 
by micro-organisms, such as the pneumococcus, 
staphylococcus and the influenza bacillus. Many 
soluble poisons, aconite, diphtheria toxin and the 



140 



INFECTION AND IMMUNITY. 



toxin of hay fever are readily absorbed from the 
conjunctiva. 
Nasal Cavity. Compared with the anterior nares, the posterior 
are poor in micro-organisms. This, in part, at 
least, is due to the tortuosity of the channels, caus- 
ing dust and bacteria to strike the walls where 
they are held by a moist surface, and the action 
of the ciliated epithelium in carrying them imbed- 
ded in mucus, again toward the anterior nares. 
Nevertheless, the nasal mucous membrane is a 
common infection atrium for streptococci, staph- 
ylococci, diphtheria and influenza bacilli, the dip- 
lococcus of epidemic meningitis, and, probably, for 
other infectious agents. 

Month. Very many species of micro-organisms flour- 
ish in the oral cavity, some of them being patho- 
genic : staphylococci, streptococci, pneumococci, 
and often diphtheria bacilli. They are constantly 
removed with the saliva, and through the exten- 
sive desquamation of the epidermis occasioned by 
mastication. Saliva is not germicidal, but in- 
hibits the growth and weakens the virulence of 
some bacteria. The fetid breath and the sor- 
clidity observed in fevers where the mouth is dry 
are attributable at least in part to the lack of 
saliva with its anti-infectious properties. The 
great rapidity with which wounds of the month 
heal is a potent factor in preventing serious infec- 
tions. 

Lnngs. Micro-organisms do not readily reach the ulti- 
mate ramifications of the bronchioles. In ordinary 
respiration the velocity of the inspired air is so 
reduced as it nears the alveoli that the further 
movement of the gases is one of gradual diffusion 
more than of violent admixture. Consequently 



LUNGS AXD STOMACH. 141 

there are greater opportunities for germs to come 
in contact with the bronchial walls where they 
become imbedded in mucus with which they may 
be expelled by coughing and the action of the 
ciliated epithelium. Both the alveolar epithelial 
cells and the leucocytes which enter the air sacs 
and bronchioles have been shown to take up bac- 
teria. The conditions in the lungs which favor 
the development of infections, as bronchitis, pneu- 
monia, influenza, tuberculosis, are by no means 
clearly understood. Variations in individual 
resistance, here as in other parts of the body, such 
as may be caused by exposure to cold, are certainly 
of great importance. It is probable that the lung 
is the infection atrium for a number of our acute 
infectious diseases. It has been demonstrated that 
systemic infections, as with anthrax bacilli, may 
be caused by the inhalation of the micro-organisms. 

The gastric juice, through the hydrochloric stomach. 
acid it contains, is able to kill anthrax, typhoid, 
tubercle bacilli, cholera vibrio and other organ- 
isms. Clinical and experimental evidence shows 
that this power is often inadequate, virulent 
micro-organisms reaching the intestines in spite 
of it (typhoid, cholera, dysentery, tuberculosis, 
etc.). It is probable that bacteria in the stomach 
are often protected against the action of the gas- 
tric juice to some extent by being imbedded in 
solid particles of food. Certain acidophilic germs, 
as well as yeasts and torulge, seem to flourish in the 
gastric secretions; these are largely non-patho- 
genic, but the regularity with which peritonitis 
follows perforating wounds of the stomach indi- 
cates that it probably always contains pathogenic 
bacteria, though it may be only their temporary 



142 INFECTION AND IMMUNITY. 

habitat. The gastric juice may render some bac- 
teria harmless by digesting their toxins; one 
gram of the gastric juice of a dog will neutralize 
fifty fatal doses of diphtheria toxin, or 10,000 of 
tetanus toxin, using the guinea-pig as the test 
animal. On the other hand, the toxin of the bacil- 
lus of botulism (causing a form of meat poison- 
ing) seems to be uninfluenced by the stomach con- 
tents, as the development of the intoxication indi- 
cates. Vomiting is often a means of ridding the 
stomach of toxic substances, including bacteria. 
The stomach itself is exceptionally free from in- 
fections. 
intestines. The bile is moderately bactericidal for some 
germs, but, on the whole, the intestinal secretions 
have low germicidal powers; this is indicated by 
the fact that the colon contains many more bac- 
teria than the duodenum. On the other hand, 
the pancreatic juice destroys some toxins (diph- 
theria, tetanus) more powerfully even than the 
gastric juice. This ability of the pancreatic juice 
(o destroy toxic bacterial products may explain the 
more frequent occurrence of enteritis in the ileum 
than in the duodenum. The bile also has a neu- 
tralizing power for some toxins. Although a num- 
ber of pathogenic bacteria inhabit the intestinal 
tract (colon bacillus, streptococci, etc.), they do 
not often set up inflammatory processes in the 
adult. The tissues become accustomed to their 
presence. The pathogenic bacteria which do not 
normally exist in the intestines are those which, 
on introduction, are most likely to cause disease 
(typhoid, cholera, dysentery, etc.). The intesti- 
nal tract of the infant, on the other hand, is fre- 
quently attacked by some micro-organisms (strep- 



INFLAMMATION: 143 

tococcus, colon bacillus, Bacillus pyocyaneus) , 
which in the same locality in the adult appear 
harmless. The fact that many individuals are not 
stricken in an epidemic, in which all are equally 
exposed to infection, points to the probability that 
pathogenic organisms (typhoid, cholera and dys- 
entery) often traverse the intestinal canal without 
inducing disease. Naturally, microbes 'are elimi- 
nated in enormous quantities in the feces, and in 
inflammatory states this elimination is increased 
by diarrhea. It is also not to be forgotten that the 
intestinal tract is, to a considerable extent, a 
lymphoid organ, and that in the presence of infec- 
tion enormous quantities of phagocytes can be 
called into action quickly. 

The protective properties of the genito-urinarv 
surfaces are not different in principle from those 
already mentioned (vaginal acidity, mechanical 
and perhaps bactericidal cleansing by the men- 
strual flow, urinary irrigation). 

{2) Internal Protective Agencies. 
A. Inflammation. 

Although there are many chemical and physical 
agents which may cause inflammation, we are in- 
terested here only in those of an infectious na- 
ture. 

Inflammation may be considered as a reactive Nature of^ 
condition on the part of the tissues, which devel- 
ops in response to the action of some injurious 
agent. The process may be beneficial in some in- 
stances, while in others it may be pernicious from 
the beginning to the end. The thickening of the 
endothelium of the cerebral vessels as one sees it 
in syphilis is a progressive, reactive change which 



Inflammation. 



144 INFECTION AND IMMUNITY. 

in no sense can be of benefit to the individual, and 
which can have no conceivable function in over- 
coming the syphilitic infection. Likewise, the new- 
formed connective tissue seen in alcoholic cirrho- 
sis of the liver is of no benefit to the hepatic tissue, 
though it may serve in some degree to protect the 
liver cells from the alcohol which continues to be 
ingested. In an ulcer of the cornea the presence 
of serum and of leucocytes, as well as the prolifer- 
ation of connective tissue, may be the sine qua non 
for the healing of the ulcer, yet the resulting scar 
may greatly impair the vision. The inflammation 
in the instances cited is injurious because of the 
functional importance of the tissues involved. On 
the other hand, an extensive scar which has 
formed in tissues of less functional importance, 
as in the skin and subcutaneous tissue, may be 
harmless. 

It is, then, to be recognized that there are certain 
consequences of the inflammatory reaction, the 
seriousness of which depends on the situation, 
severity, duration and extent of the process, and 
that these consequences are independent of any 
protective function the inflammation may have 
exercised. 
variations The amount and character of the reaction are 
subject to man}' - variations, depending on a num- 
ber of conditions: 

1. It varies with the nature of the microbe. 
Xon-pathogenic organisms induce little more in- 
flammation than so many minute, inanimate, 
non-toxic particles. The tubercle bacillus causes 
especially the formation of connective tissue, 
giant cells and the accumulation of lymphoid 
cells, aside from some retrogressive changes char- 



in Reactions. 



LEUCOCYTES. 145 

acteristic of the disease. Organisms similar to 
the streptococcus and pneumococcus lead to the 
formation of pus and fibrin, to the accumulation 
of serum and of polymorphonuclear leucocytes 
more than mononuclears, whereas the prolifera- 
tion of fixed tissue elements is secondary. The 
tetanus bacillus alone causes almost no local in- 
flammatory change. 

2. The reaction is influenced by the virulence 
of a particular strain. A streptococcus which 
has lost its virulence is disposed of by the animal 
tissues with a minimum tissue reaction, perhaps 
no more than slight congestion and edema and 
the wandering in of a few leucocytes ; one of high- 
er virulence causes an intense reaction, mani- 
fested by congestion, edema, hemorrhages, necro- 
sis and pus formation; then streptococci of such 
great virulence that they destroy life in the course 
of a few hours are occasionally encountered in 
wound infections and in peritonitis, having in the 
meantime elicited a minimum inflammatory reac- 
tion. 

3. It has a relation to the resistance or the nat- 
ural immunity of the individual. Metchnikoff, 
in particular, has shown that animals of high re- 
sistance to a particular microbe destroy the germ 
quickly by phagocytosis, while in susceptible ani- 
mals the accumulation and activity of phagocytic 
leucocytes are deficient. 

The occurrence of leucocytes in inflammatory Leucocytes. 
conditions is so characteristic that one naturally 
seeks to associate their presence with some in- 
fluence which is exerted by the toxic substance or 
the bacteria which cause the inflammation. It is 
a long-known fact that some microbes attract one 



146 



INFECTION AND IMMUNITY. 



kind of leucocyte, that others attract another 
kind, and that in still other instances the leuco- 
cytes appear to be either uninfluenced or actually 
are repelled by the infecting agent. 
ciiemotaxis. The phenomenon of living cells moving toward 
or away from certain other cells or substances is 
an expression of affinity and this affinity is known 
as chemotaxis; the former is positive, the lat- 
ter negative, chemotaxis. There is a somewhat 
general law, but one to which exceptions exist, 
that, regardless of the microbe involved, the more 
acute the inflammatory process the more do poly- 
morphonuclear leucocytes accumulate, while in 
the more chronic infections, with much connec- 
tive tissue formation, the mononuclear leucocytes 
predominate. Thus in tuberculosis one finds 
ljTnphocytes and plasma cells — mononuclears — 
predominating greatly over the polymorphonu- 
clears. In the acute purulent infections, on the 
other hand — streptococcus, staphylococcus, pneu- 
mococcus — the latter type of leucoc}^te predomi- 
nates, the mononuclears being fewer and remain- 
ing at a distance from the center of action. There 
is reason to believe that the mononuclear leuco- 
cytes play an important, though perhaps indirect, 
role in the formation of the connective tissue. 
piiasocytosis. The ingestion of particles by living cells, phago- 
cytosis, is a property which many cells possess. 
Although micro-organisms and inanimate parti- 
cles are sometimes found in epithelial cells, cer- 
tain of the mesoblastic cells have this function 
pre-eminently : polymorphonuclear leucocytes, large 
mononuclear leucoc}^tes (lymphocytes), ameboid 
connective tissue and endothelial cells. Of these 
the polymorphonuclear leucocytes, the microphages 



PLASMA AXD SERUM. 147 

of MetchnikofT, have the greatest phagoc} T tic power ; 
the others, the macrophages, are more exception- 
ally phagocytic, but some of them take up such 
cells as erythrocytes and other tissue cells readily. 
Now, the mere ingestion of the bacteria by such 
cells would not be of necessity injurious to the 
microbes; indeed, opponents of MetchnikofFs pha- 
gocytic theory of immunity held that phagocytosis 
by wandering cells may be, and often is, pernicious, 
in that the cells may return to the circulation and 
spread the infection to other parts. This is prob- 
ably true in many instances. But when we 
learn that after ingesting the bacteria the phago- 
cytes are often able to kill and digest them, it is 
realized that the process may be a genuine pro- 
tective factor. This being true, the importance of 
positive chemotaxis in recovery from an infection 
becomes manifest. It is also represented that 
phagocytic cells have the power of excreting their 
germicidal substances into the plasma and serum 
and lending to the latter a bactericidal power. 
Furthermore, it is held that they may absorb liquid 
poisons, bacterial toxins, and in some manner de- 
stroy their toxicity. As shown later, these are es- 
sential points in the phagocytic theory of immun- 
ity. 

Serum, even when entirely free of leucocytes, 
has bactericidal powers for many micro-organisms ; 
it need not be discussed at present whether this 
power exists primarily in the serum or is one con- 
ferred on it by the leucocytes. In view of its pres- 
ence, however, it is evident that the serous exu- 
date which is usually present in inflammations, 
especially the acute, may be of influence in com- 
bating the infection. Serum mav contain natural 



Influence of 
Plasma and 
Serum. 






14S INFECTION AND IMMUNITY. 

antitoxins, and, in addition, it may be of value 
in lessening the toxicity of poisons by diluting 
them, aiding in their elimination, or destroying 
them by means of ferments ( ! ) . 
Fibrin. The abundant deposit of fibrin seen in some in- 
flammations is of mechanical value by hemming 
in the infection and by offering a barrier to the 
rapid diffusion of toxins. We are all familiar 
with the part played by fibrinous and fibrous ad- 
hesions in preventing a localized peritonitis from 
becoming generalized. In prolonged inflamma- 
tions fibrin furnishes a ground substance into 
which new connective tissue and vessels grow (or- 
ganization). 
inflammatory The new-formed connective tissue seen in many 

Connective 

Tissne. inflammations, especially the chronic, as in tuber- 
culosis and actinomycosis, offers an important 
barrier to the extension of an infection. Perhaps 
no better example of this could be cited than the 
dense tissue which forms around a tuberculous 
sinus or abscess. 

To sum up, the inflammatory reaction antago- 
nizes infections, (1) mechanically, through the 
formation of new connective tissue around the 
focus, and dense accumulations of leucocytes and 
fibrin; (2) through the bactericidal and antitoxic 
actions of the lymph and serum ; ( 3 ) through the 
phagocytic action of ameboid cells. 

The value of hot applications, and Biers passive 
congestion treatment, in local inflammations, finds 
a logical explanation in view of the facts men- 
tioned, in that they increase congestion, which 
hastens the exudation of plasma and leucocytes 
and the proliferation of cells, and accelerate the 
elimination of toxic substances. 



NA TUBAL IMM UNITY. 



149 



The special features of the phagocytic theory of 
immunity are considered in a later chapter. For 
many details in regard to inflammation, the reader 
is referred to the classic article of Adami on this 
subject in the first volume of Allbutt's "System of 
Medicine." 

B. Properties of the Serum and Plasma. 

We have seen that the protection afforded by 
the body surfaces may be effective against both 
microbes and their toxins, and that local inflam- 
matory processes, although most certainly antago* 
nizing the bacteria, may at the same time have 
some antitoxic value. 

The term "natural immunity/ 7 however, as indi- 
cated in the preceding chapter, has a peculiar appli- 
cation to the natural resistance of some species or 
races of animals to infections to which other spe- 
cies or races are susceptible ; and to an unusual in- 
dividual resistance often seen in members of a 
given race or species. This condition depends on 
properties residing in the tissues or fluids of the 
body, and consequently is independent of any pro- 
tection which the body surfaces afford. Its pres- 
ence is demonstrated in the most striking man- 
ner by the experimental method, when micro-or- 
ganisms or toxins are injected directly into the tis- 
sues or circulation. At the same time every-day 
observation provides many examples. 

In certain instances natural immunity or sus- 
ceptibility shows a relation to zoological affinities. 
Thus only man and the higher apes are susceptible 
to syphilis; and only animals which are closely 
related to cattle, as sheep, goats and other rumi- 
nants, suffer from rinderpest. There are many 



Natural 

Immunity. 



Zoological 
Relation- 
ships. 



150 INFECTION AND IMMUNITY. 

exceptions to this tendency, however; perhaps the 
most striking example is found in the fact that 
whereas sheep ordinarily are extremely susceptible 
to anthrax, Algerian sheep are relatively immune. 
Similarly the white rat is immune (relatively) 
and the wild rat is susceptible to anthrax. 
Factors in Natural immunity may depend on a lack of 
immunity, pathogenicity on the part of the organism for the 
host, which is equivalent to insusceptibility on the 
part of the host; or, on the presence in the host 
of a sufficient quantity of antibacterial and anti- 
toxic substances; or, as suggested by Ehrlich, on 
the inability of the micro-organism to proliferate 
in the host because proper nutritive substances are 
not present, or, if present, are bound to other sub- 
stances in such a way that they are not available as 
food for the organisms. 

As stated in the preceding chapter, immunity 
may be either antibacterial or antitoxic, i. e., the 
immunity may in one case depend on the power 
of the animal's tissues and fluids to destroy the 
micro-organisms, or, in another, on their power 
to neutralize or destroy the bacterial toxins. 

The distinction between antibacterial and anti- 
toxic immunity is demonstrated more readily in 
acquired than in natural immunity. When one 
has recovered from typhoid fever, for example, his 
serum has acquired an increased power of killing 
the typhoid bacillus, while at the same time it 
appears to have little or no power of neutralizing 
the poisons of this organism. Acquired immunity 
to diphtheria, on the other hand, is characterized 
by the power of the serum to neutralize the toxin 
of the diphtheria bacillus, although it hardly 



TYPES OF IMMUNITY. 151 

exceed? normal serum in its bactericidal power for 
the bacillus itself. 

Having ascertained by observation or experi- Deiemiina- 
ment that a certain species has a degree of immun- Types of 
ity to an infection, certain lines of investigation mmunit ^- 
may be followed for the purpose of determining 
the character of the immunity. If the animal 
fails to become infected following the injection 
of a living and virulent culture, it is fair to assume 
that the organisms have been killed within the 
body of the animal. That this has been the result 
ma} 7 , indeed, be determined by microscopic exam- 
ination of the different tissues and by the inocula- 
tion of culture media. It is often desirable to 
determine the extent to which micro-organisms 
are eliminated through the excretions (urine and 
feces) ; this is best done by the culture method, 
but it is often a difficult technical problem. 

The natural antibacterial forces with which we 
are familiar consist of the germicidal action of 
the serum and plasma, and the phagocytic and 
destructive action of the leucocytes, endothelial and 
perhaps other cells. It is difficult to obtain sat- 
isfactory results by a study of these forces within 
the body of the animal, particularly as regards the 
bactericidal action of the serum and plasma, hence 
such studies are usually carried on outside the 
body. Such experiments are open to the criticism, 
however, that the artificial conditions are far 
removed from those of the body, and that the 
results do not always justify us in drawing con- 
clusions regarding the course of events within the 
body. Phagocytosis under natural conditions is 
more susceptible to study, and it is to be remem- 
bered that Metchnikoff came to his far-reaching 



152 INFECTION AND IMMUNITY. 

conclusions regarding the importance of phagocy- 
tosis purely from a study of the process in vivo. In 
spite of this we have come to a better understand- 
ing of the mechanism of phagocytosis by studies 
of the phenomenon under artificial conditions, as 
will appear later. 
Germicidal In determining the germicidal action of serum, 
serum, which should be freshly obtained, it may be 
mixed with a suspension of the microbes in a 
number of test-tubes, varying amounts of serum 
being used with constant amounts of the bacteria 
in the different tubes. At a subsequent period, 
from three to twenty-four hours later, cultures on 
Petri plates are made from these mixtures. The 
numbers of colonies which appear in these cultures, 
compared with the number which appear when 
serum is not added, is an index of the bactericidal 
power of the serum. If this power is found to be 
high, it is, in the present state of our knowledge, 
considered as presumptive evidence that the nat- 
ural immunity of the animal depends on it, at 
least in part. It is, nevertheless, a fact that the 
antibacterial immunity of an animal does not 
always go hand in hand with the bactericidal power 
of its serum. A well-known illustration of this is 
the following: Both the dog and the rat have a 
rather high degree of immunity against infections 
with the anthrax bacillus; yet it has been found 
that the serum of the dog has almost no bacteri- 
cidal effect on this microbe, while that of the rat 
has a very strong effect. At the same time we 
should remember that the bactericidal power of the 
serum does not necessarily represent the entire 
antibacterial function of the body. In the serum 
we have none of the body cells, and especially none 



OPSONINS. 153 

of the phagocytes, the destructive action of which 
on some bacteria is well known. Many micro- 
organisms, indeed, which are not destroyed by 
serum at all, are readily ingested and killed by 
leucocytes (staphylococci, streptococci). 

As a consequence of fundamental studies by Phagocytosis 
Deirys and Le Clef, by Leishman, by A. E. Wright 
and others, it is now possible to study phagocytosis 
in vitro with a degree of accuracy not to be approx- 
imated in the living body. It has been learned that 
leucoc}i;es, as a rule, are not able to take up bac- 
teria until the latter have been acted on (sensi- 
tized) by some substance which is contained in the 
serum. Wright gave the name of "opsonins" to 
these substances. Some of them are susceptible to 
heat (55 C), while others are much more resist- 
ant. To the latter, which are greatly increased by 
infection or artificial immunization, Neufeld has 
applied the term "bacteriotropins." 

Leishman's method is to mix a suspension of 
the bacteria with defibrinated blood (containing 
leucocytes), incubate the mixture for fifteen or 
more minutes, to make and stain spread prepara- 
tions on slides, and then count the number of bac- 
teria which have been ingested by the leucocytes. 
The average number taken up by fifty or more leu- 
cocytes constitutes the "phagocytic index." Wright 
has varied this technic in order to study the opson- 
ins quantitatively, as will be described later. 

Experiments have shown that all normal serums 
contain opsonins for a variety of micro-organisms, 
and all micro-organisms are susceptible to phagocy- 
tosis by the blood of one or more animals, in case 
their virulence is not excessive. We have every 
reason, therefore, to believe that phagocytosis is 



154 INFECTION AXD IMMUNITY. 

an important natural protective factor, and in 
some instances it is the only one which can be 
actually demonstrated, as in the case of staphylo- 
cocci and streptococci. 

That organisms are often destroyed after being 
ingested by the leucocytes is manifest from changes 
in form which they undergo, and from the loss of 
their staining power. Cultivation experiments 
have also shown that the leucocytes are able to 
kill certain bacteria. In such experiments, the 
technic which was mentioned in testing the bac- 
tericidal power of serum may be used, in this case, 
however, substituting defibrinated blood, which 
contains leucocytes, in place of the serum. If the 
bactericidal power of the defibrinated blood is 
greater than that of the serum alone, the effect of 
the leucocytes becomes apparent. 
Alexins. At a time when the antitoxic action of serums 
was not appreciated, Buchner gave the name of 
alexins (from the Greek, &k£friv 3 to ward off) to 
the protective substances of the serum, i. e., to the 
bactericidal substances, making the observation 
that they were very labile substances, losing their 
power spontaneously in a few days when exposed 
to the air and light, or when they were heated at 
55 C. for thirty minutes. As will be indicated 
later, the "alexins" are more complex than Buchner 
supposed. 
Natural ^ n determining the presence or absence of anti- 
i Anti n*it ic ^- 0X ^ C i mmun ityj the toxin of the microbe, of 
course, must first be in hand. The methods of ob- 
taining toxins will be referred to later. If the 
animal resists a dose of toxin which, in proportion 
to weight, produces disease in some other suscepti- 
ble animal, the tissues or fluids of the first animal 



AXTITOXIC IMMUNITY. 155 

may, or may not, contain antitoxin. If the resist- 
ance is referable to the presence of antitoxin, the 
latter may be detected in the following manner: 
The animal is bled, its serum collected from the 
clot, then mixtures of the serum and of the toxin 
are injected into animals of known susceptibility 
for the toxin. If the test animal is in this way 
protected from an otherwise fatal dose of the toxin, 
it is evidence that the serum contains an antitoxic 
substance. On the other hand, if the serum shows 
no such antitoxic effect, we must conclude that the 
resistance of the animal is due to other causes; as, 
for example, non-susceptibility of the tissues, 
power of the living cells or ferments to destroy the 
toxin, or absorption of the toxin by tissues of sec- 
ondary importance to life. 

Following this method of experimentation, if 
antibacterial properties are found to the exclusion 
of antitoxic, the immunity is considered to be an- 
tibacterial; and with the converse result it is anti- 
toxic, or dependent on non-susceptibility. It is, of 
course, conceivable that in a given case it might be 
both antitoxic and antibacterial. In dealing with 
diseases of which the specific microbe is known 
and cultivated, the existence of antibacterial or of 
antitoxic substances can usually be found by the 
methods described. If the etiology is unknown, or 
the micro-organism cannot be cultivated, as in 
scarlet fever, measles, etc., that is, if the virus and 
its toxin cannot be obtained in quantities, the 
nature of the resistance is not at present open to 
determination. 

It is seldom that natural resistance is absolute. 
Pasteur found that the great immunity of the 
chicken for anthrax could be overcome by im- 



156 



IXFECT10X AXD IUMUXITY. 



Relative 

immunity. 



Non-suscep- 
tibility. 



Cell 
Receptors. 



mersing the animal in cold water, the reduction 
in body temperature supposedly decreasing the re- 
sistance. It was stated previously that physical 
exhaustion, hunger and exposure to cold may also 
reduce natural resistance. Pestilence and famine 
often go hand in hand. 

Similarly, immunity to toxins usually is rela- 
tive. As an illustration of natural immunity to 
toxins, the following table serves a good purpose. 
The horse is the animal of greatest susceptibility 
to tetanus toxin. If the minimum fatal amount of 
one gram of horse weight is taken as a unit, this 
scale of resistance for some other animals is 
obtained (Knorr) : 

For 1 gram of guinea-pig weight 2 units are fatal 

For 1 gram of goat weight 4 units are fatal 

For 1 gram of mouse weight 13 units are fatal 

For 1 gram of rabbit weight 2,000 units are fata 

For ] gram of chicken weight 200.0C0 units are fatal 

In view of the high immunity of the chicken 
against tetanus, one may be led to suppose that its 
serum would contain a large amount of antitoxin, 
yet experiments show that it possesses practically 
no tetanus antitoxin. This fact suggests that 
there is a distinct type of natural immunity 
which, it is thought, may be independent of both 
the antibacterial and the antitoxic properties of 
the body. 

It is now thought that the toxic elements of bac- 
teria are chemical substances (very complex, 
surely) which are able to injure the tissues, i. e., 
to cause disease, only by entering into chemical 
union with substances which the cells contain. 
Such chemical substances or groups, pertaining 
to the cells, will be referred to later under the 
name of cell receptors. Accordingly, if the cells 



CELL RECEPTORS. 157 

of an animal do not possess groups or receptors 
which are capable of forming a chemical union 
with the toxin, the latter would be unable to pro- 
duce injury, i. e., the animal would be immune 
even in the absence of ail bactericidal or antitoxic 
properties. This condition, however, is not one 
which is capable of satisfactory demonstration, 
at least at present, but the conditions point irre- 
sistibly to its existence in some cases. 

We are accordingly led to the conclusion that 
immunity to toxins is not in all cases antitoxic, 
in the sense that the serum contains demonstrable 
antitoxin; and likewise that immunity to bacteria 
is not in all cases antibacterial, in the sense that 
the serum contains substances which are able to 
kill the bacteria in test-tube experiments. Non- 
susceptibility and phagocytosis may be of impor- 
tance in resistance of this type. 

There is another factor, however, which may importance 
throw light on the type of natural immunity just Attacked? 811 * 
considered. We know that tetanus toxin causes 
tetanus through its power of uniting with the 
nerve cells, and we may consider that tetanus is 
a very fatal disease, primarily because of the vital 
nature of the tissue which it attacks. Now, if the 
toxin, instead of uniting with the cells of a vital 
organ, were to combine with cells of less impor- 
tance to the economy, as, for example, the cells 
of the subcutaneous tissue, it is probable that we 
should have no tetanus. In some of the lower ani- 
mals there is reason to believe that the toxin of 
tetanus does unite with such tissue (Metchnikoff). 
Roux and Borrel believe that the greater degree of 
immunity to tetanus which the rabbit has over the 
guinea-pig is due largely to the fact that the rab- 



• 158 INFECTION AND IMMUNITY. 

bit's liver is able to fix a great deal of the toxin. 
And Metchnikoff has found that the liver of the 
scorpion, which has an absolute immunity to tet- 
anus, absorbs the toxin and retains it for months. 
Summary. vv/ e may, then, enumerate the following as the 
factors which probably are responsible for the dif- 
ferent grades of natural immunity and suscepti- 
bility to various bacteria and their toxins: the 
bactericidal and antitoxic powers of the serum and 
plasma; the destructive effects of the phagocytes 
and other cells on both bacteria and toxins; a pos- 
sible absolute non-susceptibility in some cases (the 
absolute non-existence of suitable cell receptors) ; 
the lack of suitable available food for the micro- 
organisms in some instances (atreptic immunity; 
see the preceding chapter) ; the overwhelming dis- 
tribution of the "suitable" cell receptors in organs 
of less vital necessity for the individual, thus 
diverting the poisons from the more important 
organs. 

This knowledge is very general, however, and in 
many specific instances we continue to be in doubt 
regarding the exact conditions which are respon- 
sible for natural immunity and susceptibility. We 
have no reason to believe that any one factor is 
operative for all infections, although phagocytosis 
appears to be more general in its action than the 
other processes mentioned. Each disease must be 
studied as a unit in relation to each species of 
animal. In one instance the resistance or suscepti- 
bility may depend on the bactericidal power of the 
body fluids; in another, on the germicidal action 
of the leucocytes and other cells ; in another, on the 
antitoxic (destructive) action of the cells or fer- 
ments with or without the presence of true "anti- 



HEMOLYSIS. 159 

toxins" in the serum, etc. There is reason to 
believe that two or more different protective proc- 
esses may come into operation at the same time 
against a given infection. 

Eegarding natural antitoxic immunity, it seems 
probable that we have no example in which 
the resistance can be satisfactorily explained solely 
by the quantity of "antitoxins" which are dem- 
onstrable in the serum ; rather we must assume the 
existence of other means of destroying and resist- 
ing toxins, as mentioned above. 

In order that a pathogenic organism may pro- 
duce a progressively fatal disease in a susceptible 
animal, the following obstacles must be sur- 
mounted: The strong defenses of the body sur- 
faces must first be overcome ; a local inflammatory 
reaction which may have been excited must first 
prove itself to be inadequate for the limitation of 
the infection; there must be an insufficient supply 
or insufficient activity of antimicrobic and anti- 
toxic processes in the body fluids and cells. 

Other Properties of Normal Serums 

In addition to the bactericidal and antitoxic ac- Hemolysis. 
tion of many normal serums, they often possess 
other characteristics which are of the highest in- 
terest in the study of immunity. In earlier days 
it had been noted that the transfusion of blood 
from one species to another was often fatal to the 
injected animal. Later investigations showed 
that this was due to toxic substances in the trans- 
fused blood ; substances which agglutinated and de- 
stroyed the red blood cells of the injected animal. 
The process, in which the hemoglobin is dissolved 
out of the red blood cells, may be reproduced in 



INFECTION AND IMMUNITY. 



Cytotoxins. 



Agglutinins. 



Precipitins. 



test-tube experiments by mixing tbe blood cells of 
one animal with the serum of another which is 
toxic (e. g., rabbit blood + go&t serum). This is 
the phenomenon of hemolysis, and the appearance 
of such a tube is exactly like that seen when blood 
is mixed with distilled water or even with tap 
water; i. e., it is a laking of the blood, it loses its 
opacity and assumes a beautiful cherry-red color. 
The serum of practically every species contains a 
hemolytic substance (a serum hemolysin) for 
some kind of erythrocyte. 

Some serums also contain toxic agents for other 
cells; they are generally called serum cytotoxins. 
The serum of the eel not only contains a strong 
hemolysin, or hemotoxin, but also a powerful 
poison for nervous tissue, neurotoxin. Similarly 
we have normal leucotoxins for leucocytes, nephro- 
toxic for kidney tissue, etc. 

Another property of many normal serums is 
that which causes agglutination or clumping of 
bacteria, as one sees it in the Gruber-Widal test 
for typhoid. Even normal human serum may ag- 
glutinate the typhoid bacillus, but to a less degree 
than that of a typhoid patient. 

One serum often causes a precipitate in the 
serum of another animal, or in a bacterial culture 
filtrate. 

In many instances, a foreign serum which is 
not particularly toxic on first injection, becomes 
very poisonous when administered (subcutane- 
ously) a second time. (See "Anaphylaxis/') 

In considering these facts, one becomes con- 
scious of the great complexity of that substance 
which plays so important a part in immunity and 
its studv — i. e., the blood serum. 



CHAPTEE X. 



ACQUIRED IMMUNITY. 

Acquired immunity may be either active or pas- 
sive: active when it arises as a consequence of 
infection or artificial immunization (vaccination) ; 
passive, when protective or curative serums are 
injected. 

One who has recovered from scarlet fever, small- ^JJJJJSitty 
pox, plague, typhoid fever, etc., becomes possessed 
of lasting protection against subsequent attacks. On 
the other hand, the immunity afforded by an at- 
tack of certain other diseases usually is of shorter 
duration: cholera, diphtheria, pneumonia, etc. So 
far as known, the acquired protection is specific 
in character : that is, a person who has had measles 
may still have scarlet fever ; or an attack of cholera 
does not protect against a later attack of typhoid. 

In a number of diseases one attack confers no 
evident protection against a second: gonorrhea, 
influenza, recurrent fever and malaria. Some dis- 
eases may create a predisposition for recurrence: 
erysipelas, influenza, diphtheria in some instances, 
although a natural susceptibility of the individual 
may explain repeated attacks. The mere fact of 
recovery, however, is sufficient evidence of at least 
a temporary immunity. It is evident, therefore, 
that among the various infectious diseases different 
grades of active immunity must be recognized. 

Certain chronic diseases are of particular inter- 
est in this connection, as pointed out in Chapter 



162 INFECTION AND IMMUNITY. 

VII. On first thought it would seem that immun- 
chronic ity can have no place in an infection of long dura- 
tion, from which recover}' is rare or does not occur. 
This, however, is not necessarily true, and the very 
chronicity of the infection may in some instances 
depend on the establishment of a certain degree of 
acquired immunity. It is, of course, possible that 
in other instances chronicity depends on a low 
degree of virulence on the part of the micro- 
organisms or a low natural susceptibility on the 
part of the host. Sleeping sickness may be taken 
as an example of a chronic disease, the prolonged 
course of which, in all probability, depends on the 
formation of protective substances. This is indi- 
cated from the fact that an acute is followed by a 
chronic stage. At the height of the acute stage 
trypanosomes are very numerous in the blood, but 
after a time their number decreases and eventually 
it is difficult to find them except in organs which 
serve as reservoirs for them. Ehrlich speaks of 
this type of immunity as Immunitas non sterili- 
sans. It may disappear more or less completely, 
its disappearance being marked by a recurrence of 
acute trypanosomiasis. 

The existence of this temporary immunity to 
trypanosomiasis was demonstrated in mice by 
Franke. When mice, infected with mal de caderas 
(a variety of trypanosomiasis) are given an injec- 
tion of a sufficient quantity of "trypanrot," all the 
trypanosomes are killed and the cure is immediate. 
If a smaller quantity of "trypanrot" is injected, it 
may still be sufficient to free the circulation from 
parasites for twenty or thirty days, after which 
general invasion again occurs. During this period 
of comparative freedom from parasites the animals 



PERIODIC IMMUNITY. ]63 

are relatively immune, which is shown by inability 
to reinfect them with trypanosomes of the same 
species. After this period is passed they succumb 
very quickly. That the heightened resistance is 
not due to the presence of a residuum of "trypan- 
rot" in the body is shown by the fact that suscepti- 
bility for other species of trypanosomes (as 
nagana) is retained. In other words, this tem- 
porary immunity is somewhat, if not absolutely, 
specific. It probably is brought about by rapid 
active immunization consequent on the disintegra- 
tion of many parasites following the administra- 
tion of the "trypanrot." 

The conditions in syphilis and piroplasmosis 
would seem to be similar to that in sleeping sick- 
ness; i. e., during and following general invasion, 
reinfection from without does not occur, although 
the disease is still active in some part of the body. 
In both syphilis and trypanosomiasis reinvasion 
from within may occur, presumably following the 
disappearance of the temporary immunity. 

In still another infection, relapsing fever, it periodic 
would seem to be similar to that in sleeping sick- 
and reinvasion alternate before the course is com- 
pleted. It is not clear why the micro-organisms 
are not entirely killed off during the periods of 
temporary immunity. Several factors may be 
involved. During the periods of remission the 
spirilla leave the general circulation and are found 
in some of the solid organs, particularly the spleen. 
At this time they may be protected to some degree 
by an existence in organs which are relatively free 
from germicidal agents. During this period also 
the less resistant organisms may be destroyed and 
those which remain may undergo an adaptation to 



Immunity* 



Bacterial Infec 



164 INFECTION AND IMMUNITY. 

the protective agencies of the host, which would be 
equivalent to an immunization against the anti- 
bodies of the host. The recurrence of general 
invasion may also coincide with a disappearance of 
the general blood immunity. 
protozoan Concerning such chronic infections Ehrlich may 
be quoted ("Chemotherapeutische Trypanosomen- 
Studien," Berl. klin. Wchnschr., 1907, No. 9-12) : 
"In accordance with the views which Eobert Koch 
has developed regarding malaria, I assume that in 
various protozoan diseases an immunity of perma- 
nent character is far from occurring as readily as 
in the majority of the bacterial diseases, and that 
a certain degree of permanent immunity, charac- 
terized by the presence of antibodies, is obtained 
only after prolonged invasion of the bod}-, demand- 
ing particularly a large number of recurrences. 
If the immunity attained is not sufficient to 
destroy all the parasites, those which remain 
accommodate themselves to the injurious agents 
which are present/' 

It has, indeed, been suggested that a general 
principle prevails to the effect that any infection 
in which an attack confers strong and lasting 
immunity must be bacterial rather than protozoan 
in its etiology. This does not imply, of course, 
that all bacterial diseases confer strong immunity; 
there are many examples to the contra^, as already 
stated, although a sufficient number of examples 
are known to render it of suggestive value in the 
study of diseases of unknown etiology. 

A very important factor for progress in artifi- 
cial immunity was the knowledge that even a light 
attack of an infection (scarlet fever, cholera, 
typhoid, smallpox) may be efficient in conferring 



VACCINATION. 165 

immunity. Such light attacks are frequently 
noted sporadically and in epidemics, while occa- 
sionally an epidemic is mild in character through- 
out. Epidemics of benign smallpox occur fre- 
quently. In these instances it seems probable that 
the mild character of the disease depends on the 
low virulence of the strain which causes the infec- 
tion; and the condition suggests the possibility of 
artificial attenuation of virulent micro-organisms 
for the purpose of inducing at will infections of a 
benign character. 

It might be possible so to modify the virus that vaccination. 
protection could be established without setting in 
motion the actual disease even in a mild form. 
An attenuation of this nature had long been prac- 
ticed with smallpox virus. Before cowpox was 
resorted to as a source of vaccine, it had been the 
custom to inoculate the genuine virus of smallpox, 
for the purpose of producing immunity. Con- 
trary to the natural expectation, this method, 
instead of reproducing severe smallpox, often 
caused the modified disease called variola inocu- 
lata. This phenomenon may depend on the fact 
that the virus finds the skin and subcutaneous 
tissue an unfavorable medium for the development 
of virulence; a condition which would be equiva- 
lent to an attenuation of the microbe. The patho- 
genicity of the cholera vibrio in animal experi- 
ments is affected similarly in subcutaneous injec- 
tions. It is now generally considered that cowpox 
is smallpox which has suffered a decrease in viru- 
lence because of its passage through the cow. 
Consequently, when this weakened virus is planted 
in the skin of man, where it may undergo further 
attenuation and produce the mildest possible form 



166 INFECTION AND IMMUNITY. 

of modified smallpox, we have an ideal vaccine. 
In a similar manner the virulence of the anthrax 
bacillus for sheep may be lessened by passing the 
organism through the dove. This method of de- 
creasing, or in some cases of increasing, the viru- 
lence of a micro-organism was referred to in Chap- 
ter VII under "passage." 
Attenuation. N single method of attenuation is suitable 
for all organisms. Pasteur found that cultures 
of the bacillus of chicken-cholera become so weak- 
ened when exposed to the action of light and air 
that they may safely be used as vaccine; also that 
the anthrax bacillus when grown at 42° C. is at- 
tenuated and does not form spores, and conse- 
quently becomes a suitable vaccine for sheep and 
cattle. Of no less interest to us is Pasteur's 
method of attenuating the virus of hydrophobia 
by desiccating the spinal cords of infected ani- 
mals (rabbits) ; the altered virus is then suitable 
for the immunization of individuals who have 
been bitten by a rabid animal. 

Work of the past decade has shown that suc- 
cessful vaccination is possible against cholera, 
typhoid and plague by the inoculation of aviru- 
lent cultures, or those which have been killed out- 
right by heat. In so far as we know the immunity 
which is caused by vaccination or protective in- 
oculation is antibacterial, or, better, antimicrobic. 
This point, however, is difficult to determine in 
relation to diseases of unknown etiology, or in the 
event that the micro-organism does not lend itself 
to the necessary experimental manipulations 
(smallpox, hydrophobia). It is possible that the 
protection may be largely antitoxic in some 
instances. In Wright's method of the therapeutic 



The Serum 
in Active 



SERUM IN ACTIVE IMMUNITY. 167 

inoculation of killed cultures or bacterial products 
(e. g., staphylococci, tuberculin) the attempt is 
definitely made to increase the opsonins and other 
antibodies in the patient's blood. 

One may ask if acquired immunity to bacteria 
and to toxins is due to the presence of the anti- immunity. 
bacterial and antitoxic substances which were 
mentioned in connection with natural immunity. 
Although normal serum is strongly bactericidal 
for the typhoid bacillus, the serum of one who has 
recovered from typhoid fever possesses this power 
to a much greater degree. As this is true in many 
other bacterial infections, the new resistance is 
held to depend on the increase of bactericidal sub- 
stances in the serum. Similarly in acquired im- 
munity to diphtheria and to tetanus, the most 
conspicuous change is a great increase in the cor- 
responding antitoxins. The result is the same, 
regardless of whether the immunity be produced 
by a natural attack of the disease, or by artificial 
immunization with the specific microbe or toxin. 
Accordingly it seems probable that acquired im- 
munity in these instances depends on the presence 
in the serum of an increased amount of properties 
which, to a certain degree, may be present nor- 
mally. On the other hand, acquired immunity is 
not always represented by an increase in the bac- 
tericidal or antitoxic power of the serum. Bac- 
tericidal antibodies may, indeed, be formed, but, if 
so, the micro-organisms concerned are not sus- 
ceptible to their action. 1 This is the case with the 

1. By the method of complement fixation, which will be 
explained later, it has indeed been shown that practically all 
organisms are able to cause the formation of some type of 
antibody. 



168 



INFECTION AND IMMUNITY. 



The Leucocytes 
in Active 

Immunity. 






streptococcus, staphylococcus, pneumococcus, and 
several others. 

It was stated in the section on natural immun- 
ity that the leucocytes, acting as phagocytes and 
as resorptive cells, seem to be responsible, at least 
in part, for natural resistance to an infection, and 
there is now no lack of evidence to show that they 
are of great importance for acquired immunity, at 
least in many instances. Particularly, Metchni- 
koff and his followers have provided us with many 
observations which go to prove this point. 

These investigators showed that in acquired 
immunity the phagocytes have a much greater 
capacity for ingesting and killing bacteria and for 
absorbing and destroying toxins than when the 
animal is in a state of greater susceptibility. It is 
also concluded that the serum in active immunity 
owes its new or more powerful antibacterial, anti- 
toxic and other properties to the leucocytes, which 
under the influence of the infection have produced 
these substances in excess and excreted them into 
the plasma. 
opsonins. The views of Metchnikoff regarding the impor- 
tance of phagocytosis have been greatly strength- 
ened in recent years as a consequence of quantita- 
tive studies of phagocytosis in vitro. As already 
stated, phagocytosis of bacteria depends on their 
first being "sensitized" by the opsonins which are 
present in the serum. In 1895, Denys and Le 
Clef demonstrated that the serum of animals 
which had been immunized with streptococci 
induced a much greater phagocytosis and destruc- 
tion of these organisms than normal serum, deter- 
mining their results by means of plate cultures 
and microscopic studies. More recently, by means 



PASSIVE IMMUNITY. 



169 



of the technic evolved by Leishman and by 
Wright, this principle has been found to have a 
wide, almost universal application : in other words, 
active immunization, as in a natural infection or 
by the injection of bacterial cells, is almost invari- 
ably accompanied by an increase in opsonins, which 
appears to coincide with an increase in the phago- 
cytic power of the blood. 

Inasmuch as it has proved possible by the pro- 
longed immunization of animals with bacteria or 
toxins to induce a high concentration of antibac- 
terial or antitoxic substances in their serum, it 
was the natural expectation that if such serums 
were injected into other animals the latter would 
thereby be endowed with an increased resistance 
to the infectious agent against which the serum 
had special activities (passive immunization). 
This has been found to be the case with many 
antibacterial (typhoid, cholera, plague, dysentery, 
etc.) and some antitoxic serums (diphtheria, teta- 
nus). Unfortunately the protection afforded by 
the injection of an immune serum is of short dura- 
tion (from two to several weeks) ; it is as if a for- 
eign substance had been injected, the fate of which 
is to be eliminated rapidly. This is in contrast 
to the condition in active immunity, in which the 
protective substances are often formed over a long 
period by the body cells. 

The school of Metchnikofr* brings the leucocytes 
into relation with passive as well as active im- 
munity. It is held that the immune serum which 
is injected is potent, because it stimulates the leu- 
cocytes to a greater phagocytic activity in the case 
of antibacterial immunity, or to a greater absorp- 



Passive 

Immunity. 



The Leucocytes 
in Passive 

Immunity. 



170 



INFECTION AND IMMUNITY. 



"Stimnlins" 
and Opsonins. 



Summary. 



tion and destruction of toxins in the case of anti- 
toxic immunity. 

It is now known, as stated, that an immune 
serum favors phagocytosis because of its action on 
the bacteria rather than on the leucocytes; hence 
the position of MetchnikofFs "stimulins/"' which 
were supposed to stimulate the leucocytes to an 
increased phagocytosis, does not seem to be on a 
good footing at present. The value of the opsonins 
in passive immunity is, indeed, an unknown fac- 
tor; the question is hardly determined finally. 
Some of the opsonins deteriorate very quickly; 
hence they could be of no value in serums as they 
are placed on the market. Others are more resist- 
ant, and may have a certain value in passive immu- 
nization, although they probably do not approxi- 
mate in importance the bactericidal and antitoxic 
substances. 

By way of summary we may say that bacterici- 
dal substances, antitoxins and opsonins are the 
known and demonstrable factors in active immun- 
ity. It dqes not follow that all three factors come 
into play in every conceivable infection; or that if 
they do, in some particular disease, the three are 
equally important. Thus, in typhoid fever, the 
serum has an enhanced bactericidal power, and 
investigations seem to show that the opsonins are 
also increased; on the other hand, we have no 
evidence to show that acquired immunity to 
typhoid fever is antitoxic. In diphtheria and teta- 
nus, the immunity is represented by the presence 
of antitoxins in the serum, whereas the opsonins 
and bacteriolysins appear to be of less importance. 

Another condition is found in infections with 
staplrylococci, streptococci, pneumococci and some 



HABITUATION TO TOXINS. 171 

other organisms, in which the only demonstrable 
change of importance is an increase in the opso- 
nins, and with this an increase in the power of 
phagocytic destruction of the cocci. 

In some chronic infections it is possible that the 
individual shows a resistance to the bacterial 
toxins, which is on the order of habituation, or 
adaptation, and which is not represented by 
any demonstrable antitoxins. Thus, by the use 
of gradually increasing doses of tuberculin, an 
individual may eventually tolerate large doses 
which in the beginning would have been very 
toxic. 

In spite of this acquired resistance, however, 
the body appears to form no true antitoxin for the 
tuberculin. 2 After the cessation of treatment the 
resistance of the individual gradually returns to 
normal; that is to say, the cells return to their 
original susceptibility. 

The possible relation of anaphylaxis to acquired 
immunity will be discussed in the chapter on 
"Anaphylaxis." 

Mention may be made here of the well-known 
but curious phenomenon that resistance may vary 
with the age of the individual. Typhoid fever at- 
tacks the adolescent or middle-aged rather than 
the very young or very old. Active tuberculosis 
grows less common in the later decades of life. 
Then we have what are distinctively the diseases 
of childhood : after 15 years of age diphtheria, for 
example, is uncommon. Some of these instances 

2. Such a course of treatment does cause the formation 
of antibodies of a specific character, hut they appear not to 
be antitoxic in character. The "antituberculin" which Was- 
sermann recognizes by means of the method of fixation of 
complement has not been shown to be an antitoxin. 



Habituation. 



:■ 



172 INFECTION AND IMMUNITY. 

of acquired immunity may be referable to differ- 
ences in the character of the cell receptors at dif- 
ferent ages, while perhaps others are due to a slow 
immunizing process occasioned by the prolonged 
presence of non-pathogenic amounts of the proper 
micro-organisms. 

Emmerich and Loew found that many bacteria, 
produce in culture media, as well as in the animal 
bod}', substances which apparently act as ferments 
and which are able to kill not only the bacterium 
which secretes the ferment, but many others. For 
example, pyocyanase, the bacteriolytic enzyme of 
Bacillus pijocyaneus, dissolves pyocyaneus, 
anthrax, diphtheria and typhoid bacilli, the vibrio 
of cholera, the streptococcus and staphylococcus. 
These enzymes usually are not toxic, and it has 
been supposed that in the course of an infection 
they reach such a concentration in the blood that 
they destroy the bacteria which produced them, 
thus bringing about recovery. It is asserted also 
that they, either during infection or as a result of 
repeated injection of the ferment, enter into a 
somewhat permanent combination with the al- 
bumin of the body, forming the so-called "im- 
mune-proteidins," on which acquired immunity 
depends. 

It is also stated that with "pyocyanase-immune- 
proteidin" it is possible so to immunize a rabbit 
that a subsequent (twelve days) otherwise fatal 
dose of the anthrax bacillus is harmless. 

Although the effects of these "enzymes" on 
anthrax and on some other organisms have been 
confirmed by a number of investigators, their im- 
portance in acquired immunity and in the recov- 
ery from infections is very doubtful. There is the 



NON-SPECIFIC RESISTANCE. 173 

special objection to this theory that it puts im- 
munity on a non-specific basis; i. e., pyocyanase 
will protect against anthrax, diphtheria, etc., 
while, in reality, all our clinical and experimental 
data point to the high specificity of acquired 
immunity. 

In contrast to the specific immunization which 
may be accomplished with an immune serum, it is 
important to recognize that a non-specific increase 
in resistance may be caused by the injection of a 
number of substances, which in the test-tube have 
no destructive action on the bacteria. Issaeff 
injected into the peritoneal cavity such substances 
as bouillon, tuberculin and sterile urine, and found 
the resistance of the animals increased to the peri- 
toneal inoculation of virulent organisms. Normal 
serum from another animal has a similar effect, 
but, in this instance, the bactericidal substances of 
the foreign serum may be a factor in the new 
resistance. Supposedly, this non-specific resistance 
is local, and it appears to depend on the attraction 
of an increased number, of phagocytes and of addi- 
tional complement (alexin) to the peritoneal cav- 
ity. The suggestion that, preceding laparotomy, 
nucleinic acid be injected into the abdominal cav- 
ity, in order to increase the local resistance, has 
its foundation in the experimental work cited. 

The serum of an animal acquires antibodies not i mmnne 
only for bacteria and toxins, but also for many - exotoxins. 
other cells and substances which may be injected. 
There are many immune cytotoxins, such as the 
hemolysins, leucotoxins, neurotoxins, nephrotoxins, 
etc., "which are formed as the result of immuniza- 
tion with the corresponding cells. (See "Cyto- 
toxins") 



INFECTION AND IMMUNITY. 



Immune 
Agglutinins* 



Tmmune Precip- 
itins and tlie 
Biologic Test 
for Species. 



By systematically injecting an animal with a 
bacterium or with any tissue cell, agglutinating 
substances (agglutinins) are formed and may be 
demonstrated in the serum. Like other antibodies, 
they are highly specific for the cell used in the 
immunization. 

It has been found that toxins, other than those 
of bacterial origin, will yield antitoxins by im- 
munization. Such toxins are snake venom, yield- 
ing antivenin; ricin, a hemagglutinating toxin 
from the castor-oil bean, yielding antiricin, etc. 

Recently what is termed the biologic test for 
species has assumed prominence. This test may 
be illustrated : A goat is injected repeatedly with 
the serum of man. After a number of injections 
a very minute amount of this goat's serum will 
cause a precipitate when mixed with human 
serum, but not when mixed with the serum of any 
other animal (except, perhaps, that of anthropoid 
apes). The test is so delicate that when a small 
amount of old dried human blood is dissolved in 
salt solution and treated with the goat serum the 
precipitation will still occur, and in view of this 
fact, the test has become of medicolegal impor- 
tance. 

The wide distribution of this phenomenon 
among all kinds of animals gives it great biologic 
significance, particularly as regards the differentia- 
tion of species. 

Kraus found that by immunization with cer- 
tain bacterial filtrates substances are formed in 
the serum which cause precipitates in the filtrates. 
It is further interesting that other albumin-con- 
taining substances, as egg albumin or milk, will 
on immunization, yield specific antibodies. The 



AXTIFERMENTS. 175 

serum of an animal which has been immunized 
with goat's milk will cause a precipitate in the 
latter, bnt not in cow's milk. (See "Precipitins.") 

It has also been possible to obtain specific anti- Antiferments. 
bodies for ferments: for the peptonizing ferments 
of bacteria, for emulsin, lab, fibrin ferments, etc. 

There are, however, a great many substances for 
which antibodies can not be obtained; this is true 
for substances of known chemical composition, 
such as acids, bases. Raits, and for the alkaloids 
(strychnin, morphin, aconite, etc.) 



CHAPTEE XI 



TOXINS AND ANTITOXINS. 

Ehriicu-s Through Ehrlich the word toxin has come to 
of Toxin, have a special significance, being applied only to a 
certain type of toxic substances. According to his 
original conception they have the following prop- 
erties : 

1. They are extremely labile substances which 
occur as secretion products of vegetable or of ani- 
mal organisms. 

2. Their chemical nature is unknown. The im- 
possibility of obtaining them in pure form and 
their great lability render them insusceptible to 
ordinary chemical analysis. 

3. An analysis of a toxin may be reached at 
present only through the medium of biologic ex- 
periments. 

4. Immunization with toxins yields antitoxins. 
It has not been possible to obtain antitoxins for 
inorganic poisons, glucosids and alkaloids 
(morphin, strychnin, etc.) 

5. In contrast to well-defined chemical poisons, 
the action of toxins is characterized by a latent or 
incubation period. That is, following the introduc- 
tion of a toxin, a certain period of time elapses 
before toxic symptoms appear, and this period is 
greater than the time logically required for the 
absorption of the toxin through the circulation. 1 

1. ReceDt work indicates that the long incubation period 
of tetanus may depend, at least in part, on the length 
of time required for the toxin to reach the ganglion cells 
through the axis cylinders of the motor nerves. 



TOXIXS. 177 

The incubation period ma}' be shortened experi- 
mentally by the injection of large quantities of 
toxin, but it can not be eliminated entirely. The 
poisons of snake venoms appear to act without in- 
cubation period, but they are still to be classed 
with the toxins, because of their power to cause 
the formation of antitoxins. 

6. "The facts make it necessary to assume, as a 
condition for the poisonous action of toxins, a spe- 
cific chemical union of the toxin with the proto- 
plasm of the cells in certain organs." . . . "The 
affinity of other poisons, as the alkaloids, for 
tissues, depends not on chemical union, but on 
some such process as solid solution or loose salt 
formation." 

The preparation of the soluble toxins of bacteria Preparation 
is relatively simple. It is necessary only to inocu- 
late a suitable fluid medium with a culture of the 
microorganism, to allow growth to take place for 
some days at body temperature, then to pass the 
fluid through a porcelain or some equivalent filter. 
The soluble toxins usually may be precipitated 
from the filtrate by some precipitant, as ammon- 
ium sulphate, and preserved in a dried state for a 
long period. Such a precipitate does not represent 
the toxin in a pure form, but various proteid sub- 
stances of the culture medium, as well. 

The bacilli of diphtheria and tetanus, Bacillus 
pyocyaneus, and Bacillus toiulinus, are the princi- 
pal micro-organisms which produce soluble toxins. 

When the toxins of these organisms are injected 
into a suitable animal, phenomena similar to those 
produced by an infection with the organisms 
themselves are produced. They are in a particu- 



of Toxins. 



178 INFECTION AND IMMUNITY. 

lar sense specific toxins. Some micro-organisms, 
however, produce more than one toxin. The teta- 
nus bacillus, for example, secretes, in addition to 
the toxin causing the nervous symptoms of tetanus, 
another (tetanolysin, or tetanus hemolysin) which 
has the power to destroy red blood cells. Ehrlich 
holds that the diphtheria bacillus produces not 
only the toxin which causes the acute intoxication 
of diphtheria, but another of long incubation 
period which may cause paralysis. Cobra poison 
has at least two toxins, one which attacks the nerv- 
ous tissues — a neurotoxin — and another which at- 
tacks the erythroc}des ; the two may be separated 
by appropriate measures. As previously stated, 
the serum of the eel has a strong neurotoxin and 
a hematoxin. 
secondary Some micro-organisms produce one or more 

Toxins. 

soluble toxic substances, which it is often difficult 
or impossible to consider as the actual disease- 
producing elements of these organisms. Concern- 
ing a disease which is so well characterized clini- 
cally as tetanus, it is not difficult to determine 
by inoculation experiment whether one has in hand 
the specific toxin. The proof is naturally much 
more difficult in infections with streptococci and 
staphylococci, for example, in which the group of 
symptoms and the pathologic conditions are not 
entirely unique for the infection. We are by no 
means certain that the hemolysin or the leucoci- 
din (toxin for leucocytes) of the staphylococcus, 
or the hemolysin of the streptococcus are the para- 
mount disease-producing toxins of these organisms, 
although these substances are true toxins. 



i 



TOXINS. 179 

An important test for the pathogenic signifi- 
cance of a toxin lies in its ability or inability to 
cause the formation of an antitoxin which is 
efficient in the treatment of an infection by the 
corresponding organism. This is not the case 
with the toxins just mentioned. However, one 
should not place too much importance on such a 
test, for it is possible that we are not able on 
artificial culture media to obtain the toxin in 
such concentration that the production of an effi- 
cient antitoxin is possible. 

There is a large class of organisms the members intracellular 
of which apparently do not produce soluble toxins ; Endotoxins. 
such organisms, however, cause highly toxic diseases 
(e. g., typhoid, cholera, plague). The dead or 
ground-up bodies of such bacteria are very toxic; 
also when the germs disintegrate by a process of 
autolysis or self-digestion the culture medium be- 
comes toxic because of the cell contents which are 
set free. Such organisms are said to contain in- 
tracellular toxins or endotoxins. In infections by 
them it is supposed that toxic symptoms are pro- 
duced when a pathogenic amount of the intracel- 
lular toxins is liberated by the bacteriolytic action 
of the body fluids or cells (phagocytes). 

Nothing is known of the nature of such toxins. 
They certainly are very different from the soluble 
toxins of diphtheria and tetanus, since immuniza- 
tion with them has not as yet resulted in the pro- 
duction of efficient antitoxins. In spite of this 
fact, however, it is none the less probable that 
they are the disease-producing constituents of the 
organisms. Buchner gave the name of "plasmin" 
to the cell juice which he was able to express from 
some micro-organisms. 



180 



INFECTION AND IMMUNITY. 



The Mac- 
Fadyen 
Method. 



Accidental 

Toxic 

Substances. 



Preparation 
of Antitoxins. 



MacFadyen, by grinding large masses of typhoid 
bacilli and other organisms which had been rend- 
ered brittle by the temperature of liquid air, 
obtains from these organisms a toxic cell juice. 
The efficiency of the antitoxins which he is said 
to obtain by such immunization has not been 
demonstrated practically. It seems improbable 
that immunization with such "toxins" will yield a 
serum differing in properties from that obtained 
by immunization with the living organisms. 

Toxic substances obtained from bacteria by the 
action of strong chemicals and extracting fluids, 
may not represent the essential toxic substance of 
the organism, but perhaps some disintegration 
product which happens to be toxic. 

It is, of course, common knowledge that an anti- 
toxin is the blood serum of an animal, after the 
latter has been rendered highly immune by re- 
peated injections of the corresponding toxin. The 
horse is chosen for immunization because of its 
marked ability to yield antitoxins (diphtheria, 
tetanus), because of its size, withstanding much 
loss of blood, and because of the readiness with 
which it submits to manipulation. 

Manufacturing plants which produce antitoxins 
and other antiserums on a large scale have splen- 
didly equipped stables, which are kept in the 
optimum hygienic condition, and from which rats 
in particular are rigorously excluded. 2 The horses 



2. The importance of this is very great if, for example, 
horses are receiving injections of some virulent living 
micro-organism (as the plague bacillus). In this case 
living micro-organisms reach the general circulation, and a 
rat having bitten the animal could well contract the 
plague and be an evident source of danger, not only to 
other animals, but to the community at large. Even fly 
proof stalls are properly instituted in such cases. 



TOXINS. 181 

are carefully groomed and nourished and given 
such exercise as will keep them in a healthy con- 
dition. 

The toxins, in solution, are injected subcutane- 
ous^. 3 Grave and even fatal reactions may follow 
the first injections, if the toxin has been given in 
too large doses or in too concentrated solutions. 
This is especially true when injecting tetanus 
toxin. It is of great importance first to establish 
what the Germans call a "Grundimmunitat" 
which means a primary immunity in the animal 
itself so that the immunization may then be 
pushed vigorously until the blood contains anti- 
toxin in high concentration. For this purpose it 
has been found necessary to weaken the first tox- 
ins injected. This may be done by heating the 
toxin solution to 65 or 70 C. for an hour; by add- 
ing to it from 0.05 to 0.4 per cent, of the trichlo- of Toxins. 
rid of iodin; or by adding a solution of potassium 
iodid in which iodin has been dissolved (Lugol's 
solution) or, as is often done at present, by par- 
tially neutralizing the toxin with antitoxin. High 
dilutions of the unaltered toxin may also be used. 
Gradually the virulence and amount of the toxin 
injected may be increased until finally the full 
virulent toxin is given in large doses. The increase 
in dosage must be very gradual. Eventually as 
much as a liter or more of diphtheria toxin is 
tolerated. 

Following each injection a reaction occurs. 
With diphtheria the local swelling may be great, 
and sloughing may occur. Following an injection 

3. For the production of antivenin the snake venom Is 
best injected intravenously. 



Attenuation 



182 INFECTION AND IMMUNITY. 

of tetanus toxin, tetanic symptoms may appear. 
In either case, there is some loss of weight and 
often fever, and another injection must not be 
given until the original weight is regained and 
the general behavior of the animal indicates that 
its former healthy condition is re-established. 

Several months of such treatment are necessary 
for the production of diphtheria antitoxin in high 
concentration. At the end of this time blood is 
drawn from the jugular vein by means of a large 
trochar to which a rubber tube is attached. The 
tube leads to a tall glass cylinder holding from 
one to two liters, and into this the blood is allowed 
to flow. Six liters may be drawn safely from a 
horse of average size. 4 The most rigid asepsis is 
observed in taking the blood. The glass cylinders, 
appropriately covered to prevent contamination, 
are then set in a cool, dark place, and after the 
serum has separated from the clot samples are 
taken to be tested for their antitoxic value. 
Preservatives The serum, in bulk or after being bottled for 
the trade, is preserved at a low temperature and 
in the dark, 0.5 per cent, of carbolic acid having 
been added to insure sterility. The addition of 
the acid may cause harmless cloudiness in the 
serum, but does not destroy the antitoxin. Serums 
may be preserved perfectly in a dried or frozen 
state. 

Many facts of scientific and practical impor- 
tance have been brought to light through the im- 
munization of animals on a large scale. It has 

4. Some horses may be bled as many as forty times 
without suffering a conspicuous deterioration in health. In 
time, however, an animal becomes less valuable as an an- 
titoxin producer. 



STANDARDIZATION OF SERUMS. 



been found, for example, that following each in- 
jection of toxin the amount of antitoxin in the 
blood suffers a reduction, and only equals or rises 
above the previous amount eight or ten days later. 
This decrease is explained by assuming that the 
toxin has, to a certain extent, united chemically 
with the circulating antitoxin. It indicates also 
the period at which the horse should be bled in 
order that the greatest amount of antitoxin may 
be obtained. It might even be dangerous to draw 
the blood before this time had elapsed, since some 
free toxin might still be in the circulation. 

It is noteworthy that all horses are not equally 
good producers of antitoxin. One may yield a 
serum of three times the value of another, al- 
though the two have been treated identically and 
seem to be equally immune to the toxin. 

Another most interesting fact is that, although 
the blood of an animal may be very rich in anti- 
toxin, he still may have a disproportionate sus- 
ceptibility to fresh injections of the toxin. 

Many of these phenomena have not been ex- 
plained satisfactorily. 

The necessity of standardizing antitoxins so standardiza- 
that dosage may be controlled accurately is self- ^na Anti- M 
evident. To meet this need the antitoxic unit toxins - 
familiar in practice was devised. 

Behring, and also Ehrlich, decided arbitrarily 
to consider as the antitoxic unit that quantity of a 
serum which would protect a guinea-pig from 100 
fatal doses of the toxin. Ehrlich's original method 
of testing a serum was to mix different quantities 
with 10 fatal doses of the toxin and inject each 
mixture into a guinea-pig of from 250 to 300 
grams' weight. That quantity of the serum which 



184 INFECTION AND IMMUNITY. 

protected the animal against the ten fatal doses of 
toxin contained 1/10 of an immunity unit, and 
from this result the number of units in a cubic 
-centimeter could be calculated. This method in- 
volved the use of toxin as the standard by which 
the value of the antitoxin was measured, and it 
was found to be unreliable. A toxin degenerates 
rather rapidly, retaining at the same time its 
binding power for the antitoxin; hence two tests 
made with the same serum two months apart 
might indicate different antitoxic values for the 
serum. Also 10 fatal doses of one toxin often re- 
quired more antitoxin for neutralization than the 
same quantity of a second toxin. These phenomena 
are due to the formation of toxids. (See next 
chapter.) 
standard On account of these sources of error, Ehrlich 
devised a new method in which a standard anti- 
toxin or test-serum is used as the starting point 
for the valuation of a new serum. The test-serum 
used at the Eoyal Prussian Institute for Experi- 
mental Therapy at Frankfurt, of which Ehrlich 
is the director, is a dried and powdered serum of 
such strength that 1 gram contains 1,700 immun- 
ity units; i. e., 1/1700 gm. would protect a guinea- 
pig against 100 fatal doses of a diphtheria toxin. 5 

5. In Germany the various serums are prepared by pri- 
vate individuals or corporations and manufacturers are re- 
quired to send a sample of every lot of serum intended for 
the trade to the Frankfurt Institute that its exact value may 
be determined. Each bottle eventually receives a stamp sig- 
nifying the value in antitoxin units of the contained serum. 
Moreover, samples of every lot of serum are retained in the 
institute, and from time to time these are tested ; and when 
it is found that the samples have degenerated beyond a cer- 
tain value the order is sent out to call in all serum belong- 
ing to the degenerated lot. When a manufacturer thinks 



STANDARDIZATION OF SERUMS. 185 

Any other high-grade serum would have answered 
equally well. 

The institute keeps in stock a large number of 
vials, each containing 2 grains of this dried 
serum. The air and moisture are exhausted from 
each vial and the latter is then sealed in the flame. 
Once in three months one of these vials is broken 
open carefully and the serum dissolved in 200 c.c. 
of a solution made up of equal parts of glycerin 
and 10 per cent, salt solution; hence each cubic 
centimeter of the solution contains 17 units. Dur- 
ing the succeeding three months this antitoxic 
solution is used in the comparative valuation of 
new antitoxins; the solution retains its strength 
unaltered for this period. For individual tests 
the serum-solution just described is again diluted 
seventeenfold, so that each cubic centimeter con- 
tains one unit. This adds to convenience and ac- 
curacy. 

The first step in the process is to standardize 
some diphtheria toxin in which the degenerative 
changes (toxoid formation) have come to a stand- 
still. This is done by adding so much of the toxin 
to 1 unit (1 c.c.) of the test serum that an excess 
of one fatal dose of the toxin remains unbound by 
the antitoxin. 

The quantity of the toxin which gives this re- 
sult is called the L+dose. 6 The LO dose of the 

the serum of one of his horses has a high value he may 
draw a small amount of blood from the animal and send 
the serum to Frankfurt for a preliminary test. If the 
serum is sufficiently strong he may then bleed the horse 
freely ; if it is weak he will be advised to continue the 
immunization for a time. 

6. L=Limes (Limit) : 4- is commonly used to indicate 
a fatal result. 



186 INFECTION AND IMMUNITY. 

toxin also is determined, this being the amount 
which is exactly neutralized by the unit of anti- 
toxin. The use of the two doses serves to eliminate 
subjective errors on the part of the observer. The 
L-f- and LO doses of toxin are then used to de- 
termine the value of new antitoxins. That quan- 
tity of the new serum which, when mixed with the 
L-f- dose of toxin, causes the animal to die in 
four to six days, contains 1 unit of antitoxin. If, 
for example, 1/100 c.c. accomplishes this result, 
the serum is of one hundredfold strength, i. e., 1 
c.c. would contain 100 antitoxic units. 

In accordance with the Act approved July 1, 
1902, the United States Public Health and Marine- 
Hospital Service has established a standard unit 
for this country. The unit is based on that of 
Ehrlich just described and was made by com- 
parison with the normal unit obtained from Ehr- 
lich's Institute, Frankfort a. M., Germany. 

Antitoxins are purchased on the open markets 
by officers of the Public Health and Marine- 
Hospital Service and tested in the Hygienic 
Laboratory for potency, freedom from contamina- 
tion by bacteria and chemical poisons, especially 
tetanus toxin, and finally to insure against excess 
of preservatives. 

The method of determination of potenc}*" is sim- 
ilar to that used by Ehrlich and previously 
described. 

White mice are inoculated to test for an excess 
of preservative. (Trikresol being the one most 
employed.) If the mouse shows trembling or other 
symptoms of poisoning after subcutaneous injec- 



CONCENTRATION OF SERUM. 187 

tion of 1 c.c. of serum, over 0.5 per cent, may be 
suspected. 

Other toxins and bacteria are discovered by 
intraperitoneal injection of guinea-pig. 

For therapeutic purposes, it is desirable to have 
a serum of high value in order to avoid giving too 
large quantities. Several diphtheria serums are 
on the market which have a value of 500 units to 
the cubic centimeter. It is difficult to immunize 
above this point. 

In some cases it is desirable to concentrate the 
antitoxic serum. 

Gibson has devised a means for this depending 
on the fact that the antitoxin is closely associated 
with or comprises the globulin of the serum. The 
method is as follows : 

To from 10 to 15 liters of serum, a saturated 
solution of ammonium sulphate is added gradually 
until precipitation is complete. This filtrate is 
then removed by filtration through paper and 
dissolved in 12 liters of water. It is then strained 
through gauze to remove the filter paper. The 
solution is reprecipitated with ammonium sulphate 
and the precipitate removed as before. The 
precipitate is then dissolved in 24 liters of a 
saturated solution of sodium chlorid and filtered 
through gauze. This solution is allowed to stand 
over night and the supernatant fluid removed from 
any precipitate which forms. The precipitate is 
washed with saturated sodium chlorid and the 
washing added to the first solution. 

The combined solutions are again precipitated 
with saturated ammonium sulphate solution and 



188 



INFECTION AND IMMUNITY. 



the precipitate collected on filter paper and the 
moisture pressed partially out with filter paper. 

The precipitate is then dialized in parchment 
paper in running water for three days, a small 
amount of chloroform being added as a pre- 
servative. 

One-half of one per cent, sodium chlorid is then 
added and the solution filtered twice through 
Berkefeld filters. 

In a similar way the U. S. Government has 
provided for the establishment of a legal tetanus 
antitoxin unit and the control of serum production. 

Owing to the fact that tetanus toxin is very 
stable, the toxin itself is kept for comparison 
instead of the antitoxin as in diphtheria. 

"The immunity unit for measuring the strength 
of tetanus antitoxin shall be ten times the least 
quantity of antitetanus serum necessary to save 
the life of a 350 gram guinea-pig for ninety-six 
hours against the official test dose of a standard 
toxin furnished by the Hygienic Laboratory of the 
Public Health and Marine-Hospital Service. 7 " 

That the United States government is attempt- 
ing to guard the quality of antitoxins on sale in 
our markets is apparent from the following state- 
ment : 8 

"EXAMINATION OF SERUMS MADE BY LICENSED 

MANUFACTURERS. 8 

"The act of Congress, approved July 1, 1902, entitled 

'An act to regulate the sale of viruses, serums, toxins and 

analogous products in the District of Columbia, to regulate 

interstate commerce in said articles, and for other pur- 

7. Bulletin No. 43, Hygienic Laboratory. 

8. From Rosenau, "The Immunity Unit for Standardizing 
Diphtheria Antitoxin," Bulletin No. 21 of the Hygienic 
Laboratory of the Public Health and Marine Hospital Service 
of the United States. 



EXAMINATION OF SERUMS. 189 

poses,' and the regulations framed thereunder, approved 
Feb. 21, 1903, imposed upon the director of the Hygienic 
Laboratory the duty of examining vaccines and antitoxins 
for purity and potency. 

"Accordingly purchases are made for the Hygienic Lab- 
oratory from time to time on the open market by officers 
of the Public Health and Marine-Hospital Service stationed 
in various parts of the country. The antitoxin is always 
bought from reliable druggists, who keep the product under 
proper conditions of light, temperature, etc. Several grades 
of diphtheria antitoxin made by each licensed manufac- 
turer are bought and sent to the Hygienic Laboratory by 
mail for the purposes of these tests. 

"The serums are tested not only for potency, but also to 
determine their freedom from contamination by foreign 
bacteria, and finally to insure the absence of chemical poi- 
sons, especially tetanus toxin. Note is made of the phys- 
ical appearance of the serum, and tests are made to de- 
termine whether an excessive amount of preservative has 
been added. 

"A. careful memorandum is made of the facts given by 
the manufacturer, as stated on the label, as to the num- 
ber of units contained in the package, and the date beyond 
which the contents can not be expected beyond a reasonable 
doubt to yield a specific result. Note is also made of the 
manufacturer's compliance with the law requiring that the 
product be plainly marked with the name of the article, 
and the name, address and license number of the manu- 
facturer. 

"Delinquencies that occasionally come to light in these 
examinations are at once reported to the Surgeon General, 
U. S. Public Health and Marine-Hospital Service, who 
takes the necessary steps requiring the immediate with- 
drawal of the particular lot of serum from the market and 
institutes measures to prevent a repetition of similar errors." 

"SERUM ANTIDIPHTHERICUM IN THE PHARMA- 
COPEIA. 

"The next edition of the United States Pharmacopeia, 
being the eighth decennial revision, 1900, which is to ap- 
pear shortly, will contain an antitoxic serum for the first 
time. The serum will be known officially as antidiphtheric 
serum or Serum antidiphthericum, and the unit will be 
recognized as that approved or established by the United 
States Public Health and Marine-Hospital Service. 

"The official text, which has been kindly furnished by 
Professor Remington in advance, will be as follows : 



190 



INFECTION AND IMMUNITY. 



♦SERUM ANT1DIPHTHERICUM. 

ANTIDIPHTHERIC SERUM. DIPHTHERIA ANTITOXIN. 

"A fluid separated from tbe coagulated blood of a horse 
Equus caballus, Linne, immunized through the inoculation 
of a diphtheric toxin. It should be kept in sealed glass 
containers, in a dark place, at temperatures between 4.5° 
and 15° C. (40° and 59° F.). 

"A yellowish or yellowish-brown, transparent or 
slightly turbid liquid, odorless or having a slight odor, 
due to the presence of the antiseptic used as a pre- 
servative. 

"Specific gravity: 1,025 to 1,040 at 25° C. (77° F.). 

"Antidiphtheric serum gradually loses its power, the 
loss in one year varying between 10 per cent, and 30 
per cent. Each container should be furnished with a 
label or statement, giving the strength of the anti- 
diphtheritic serum, expressed in antitoxic units, the 
name and percentage by volume of the antiseptic used 
for the preservation of the liquid (if such be used), 
the date when the antidiphtheric serum was last tested, 
and the date beyond which it will not have the strength 
indicated on the label or statement. 

"The standard of strength, expressed in units of anti- 
toxic power, should be that approved or established by 
the United States Public Health and Marine-Hospital 
Service. 

"Average dose : 3,000 units. 

"Immunizing dose for well persons : 500 units." 



CHAPTER XII. 



THE STRUCTURE OF TOXINS AND ANTITOXINS 
AND THE NATURE OF THE TOXIN-ANTI- 
TOXIN REACTION. 

Because of the impossibility of obtaining bac- Biologic 

, . -i , . • j> ,. i Analysis. 

terial toxins m pure iorm, no conception can be 
gained of their composition in terms of atoms or 
molecules, although it must be assumed that they 
have some unknown molecular structure. Infer- 
ences as to their nature and structure can be 
gained only by means of the biologic experiment, 
i. e., their effects on animals and animal cells 
under arbitrary conditions. 

When a toxin and its antitoxin are mixed in jveutraiiza- 

.. , , . . ., . . , tion of Toxin 

suitable proportions, the mixture becomes non- by Antitoxin. 
toxic as the result of chemical union of the two 
substances; each molecule of toxin has combined 
with a molecule of antitoxin to form a new non- 
toxic molecule which may be spoken of as the 
toxin-antitoxin molecule. It was at one time sup- 
posed that antitoxin had the power of destroying 
the toxin, perhaps by a ferment-like action. In 
two instances it has been possible to show that 
this is not the case. Ordinarily toxins are more 
susceptible to heat than antitoxins, but in the case 
of pyocyaneus toxin and snake venom the anti- 
toxins are the more susceptible. Wassermann 
found that when a neutral mixture of pyocyaneus 
toxin and its antitoxin was heated to a certain 
temperature the mixture again became toxic, and 
Calmette made a similar observation concerning 
venom and antivenin. If the toxin had been de- 



192 



INFECTION AND IMMUNITY. 



Chemical 
Nature of 
Reaction. 



Ferments. 



stroyed by the antitoxin the solution certainly 
would not have regained its original toxicity on 
the application of heat. 

The following facts add support to the view 
that neutralization consists of chemical union be- 
tween "tine two substances: 

First, neutralization takes place according to 
the law of multiple proportions, i. e., ten times a 
given amount of antitoxin will neutralize a pro- 
portionate amount of toxin; second, neutralization 
is more rapid at warm than at cold temperatures; 
and, third, more rapid in concentrated than in di- 
lute solutions. These are some well-known laws of 
chemical reactions. 

"Emil Fischer has shown that in the ferments, 
definite atom-groups of special configuration are 
present which above all else are requisite for the 
whole phenomenon (of fermentation). Only such 
substances as possess a group to which the ferment 
group corresponds, as lock to key, are subject to 
the action of a particular ferment." This applies 
to the action of a particular ferment on only one 
kind of substance. 
Haptophores. Having this conception in mind, Ehrlich as- 
sumes that union occurs between toxin and anti- 
toxin through a special group of atoms which the 
toxin molecule possesses, and which fits into, or 
norresponds specifically to, another group of atoms 
in the antitoxin molecule. These are spoken of 
as the binding or haptophorous groups (hapto- 
phores) of the molecules. The haptophorous 
group of the toxin molecule is highly specific since 
a toxin can be neutralized only by its own anti- 
toxin, and naturally the haptophorous group of 
the antitoxin molecule must be equally specific. 



TOXINS AXD ANTITOXINS. 



The toxin molecule contains not only a hapto- Toxophore 
phorous group, through which it unites with anti- 
toxin in one instance or, in another instance, with 
tissue cells in the production of disease, but also 
certain constituents in which the specific activity 
of the substance resides, and by which it produces 
changes in tissue cells, on combining with them. 
This functional or pathogenic- activity resides in 
this so-called toxophorous group of the molecule. 
Hence the haptophorous and tovophorous groups 
are the two structural elements of a toxin which 
may be recognized by biologic experiments. 

It is a peculiarity of toxins that they lose a cer- Toxoids. 
tain amount of their toxicity in the course of time, 
although their binding power for antitoxin remains 
practically unchanged. In the language of the 
terms which were used above, the toxophorous 
groups may degenerate or disappear and leave the 
haptophorous groups intact. Toxins which have 
undergone this change are called toxoids. 

Further evidence of the existence of toxoids lies 
in the fact that when used for immunization they 
cause the formation of antitoxins. This is possi- 
ble only when the substance is able to unite with 
the tissue cells; therefore, the non-toxic toxin or 
toxoid has retained its haptophorous groups. 

A toxin entirely free from toxoids has never 
been observed, since even during the few days re- 
quired for its preparation a certain amount of 
degeneration occurs. 

Additional information concerning the nature 
of toxin has been gained by experimenting with 
mixtures of toxin and antitoxin, in which the two 
are present in varying proportions. This is the 
"partial saturation" method of Ehrlich. Through 



Partial 
Saturation 

Method of 
Study. 



IXFEGTIOX AXD IMMUNITY. 



a vast number of experiments Ehrlich obtained in- 
. formation which permitted him to estimate that 
200 "binding units" are represented in that 
amount of diphtheria toxin (hypo the tically pure) 
which is exactly neutralized by one antitoxin unit. 
If the entire amount of antitoxin, i. e., 200/200, 
is added to the quantity of toxin in question, com- 
plete neutralization of the latter, of course, occurs. 
In case the toxin is entirely pure, 199/200 of the 
antitoxin unit would destroy all but 1/200 of the 
initial toxicity; and 150/200, or 100/200, or 
75/200, etc., of the antitoxin when added would 
permit corresponding degrees of toxicity to be 
demonstrated through animal inoculations. It 
was found, however, that neutralization did not 
take place according to this simple scale. The re- 
sults were complicated, and Ehrlich has found it 
convenient to express them graphically in the form 
The Toxin of a "toxin spectrum" (Figs. 1, 2, 3 and 4). For 
spectmm. example, let 199/200 of 'the antitoxin unit be 
added to the proper amount of the toxin, 198/200 
to another similar amount, 197/200 to another, 
etc., down to 150/200. In the last mixture, 50 
out of the 200 binding units which the toxin pos- 
sesses . are free, and these 50, rather than some 
other 50, are free because they have less affinity 
for the antitoxin than the 150 units which were 
Epitoxoicis. bound. It has been found that those units which 
first become free have a low degree of toxicity. It 
was thought that they might have lost their toxo- 
phorous groups, i. e., that they were toxoids; and 
because of their weak affinity for antitoxin they 
were called epitoxoids. It was found, however, that 
they possessed a rather constant though low degree 
of toxicity and that the toxic action was charaeteris- 



T 0X0X8. 195 

tic. Injection was followed by some local edema, Toxon. 
then by a long incubation period, and finally by 
cachexia and paralysis. On account of this char- 
acteristic toxic action and the long incubation 
period, Ehrlich has concluded that the so-called 
epitoxoid is in reality a second toxin which is se- 
creted by the diphtheria bacillus. This he now 
designates as toxon in order to distinguish it from 
that other constituent of diphtheria bouillon, the 
toxin, which causes the acute phenomena of diph- 
theria. 

The existence or non-existence of toxons has created 
a great deal of discussion among investigators. The 
Swedish chemist, Arrhenius, has recently attempted to 
apply certain principles of physical chemistry to the 
study of toxins and antitoxins. It is a well-known fact 
that some chemical substances, when in solution, have 
the power of breaking up into their constituent parts; 
thus sodium chlorid breaks up in part into sodium and 
chlorin, as sodium or chlorin ions or electrolytes. The 
dissociated sodium or chlorin may then enter into com- 
bination with any other suitable substances which may 
be present. Arrhenius holds that this is the case with 
the toxin-antitoxin molecule, that it may to a certain 
extent again break up into separate toxin and antitoxin. 
He believes that this dissociated toxin is the substance 
which Ehrlich has been calling toxon. Madsen, who 
formerly had done much work with toxons, has now 
joined with Arrhenius in support of the dissociation 
theory. Bordet believes that toxon and the various 
other constituents of toxin described by Ehrlich as 
separate substances, are the result of combinations of 
varying proportions of toxin and antitoxin. He pro- 
duced comparable phenomena by mixtures of complement 
and anticomplement in varying proportions and noting 
the degree of hemolysis produced on sensitized corpus- 
cles. In spite of the reasonableness of this theory, Ehr- 



196 



INFECTIOX AXD 11I1IUXITY. 






lich and his followers continue to uphold the toxon as 
an independent toxic substance, and have published 
additional experiments to^support their position. 

protoxoitis. Let one now add still smaller amounts of the 
antitoxin unit to the 200 binding units of the 
toxin. When 149/200 are added it is found that 
a certain amount of true toxin remains free, the 
quantity which is unbound being in direct propor- 
tion to the amount of antitoxin withheld. Conse- 
quently when but 50/200 antitoxin unit is added 
the amount of free toxin corresponds to 100 bind- 
ing units. If true toxin only remained it could 
then be said that the constitution of this toxin is: 
toxin 150 and toxon 50. However, it may be 
found that as 49/200, 48/200, etc., to 0/200 anti- 
toxin unit are added, no increase of free toxin is 
found, although the antitoxin added has been 
bound. In this case, the 50 binding units of toxin 
which have the greatest affinity for antitoxin are 
non-toxic; i. e., they are toxoids, and since they 
have the maximum amnity for antitoxin they are 
called protoxoids. 

It has been assumed also that a toxoid may 
exist which has an amnity for antitoxin exactly 
equaling that which toxin possesses; this, as yet 
purely hypothetical constituent, bears the name of 
s}mtoxoid. 

Figure 1 is a graphic representation of the 
toxin just described (Madsen). Probably no two 
toxins have the same constitution. The toxon 
zone, for example, could well be much larger in 
one diphtheria toxin than in another. 

Eefinements in experimentation show that even 
the true toxin is not uniform in its virulence and 
its amnity for antitoxin. Accordingly a proto- 



Syntoxoids. 



Proto-, Deu- 

tero- and 

Tritotoxins. 






TOXIN SPECTRA. 



197 



Protot»xo<ci 
—T—T — i — r— 


1 


Pa 

wtiilin 


i 


Toxone 

1 « 1 ■ ' 



70 ffl 91 m 110 1X0 /so ,y ,i /(0 /7tf ,^ fft tt0 

Figure 1. 



1 


11 
• 


W/i 


1 


7o * o n e 



Pr*tbU*i^ Dtunro- Tritotoxir, 
toxm , 



JJeutero- 



_ JJeucero- yr.+ + • , 




taxtni /9 

Figure 3. 



Pritotoxoid qjjBeutero, Tritotoxot'db sc 


Toxone 


T{*unx<>\a &WI Ilk 


TriT&toxaidu 


minimum 


' >v " 







Xeutero- TritcToxin $ 
Toxin, ft 

Figure 4. 

Figures 1, 2, 3 and 4 are taken from Aschoff's "Ehr- 
lich's Seitenkettentheorie, etc.," Ztschr. f. Allgem. Physiol., 
vol. i, 1902. Figure 1 is a toxin spectrum worked out by 
Madsen. Figures 2, 3 and 4 are spectra representing the 
changes in qualitative and quantitative structure which a 
toxin may undergo with age, as described in preceding para- 
graphs. 



19S INFECTION AND IMMUNITY. 

toxin, a deuterotoxin and a tritotoxin may be rec- 
ognized by this same partial saturation method. 
(See Fig. 2.) For example, it may be found that 
when a portion of the antitoxin unit, between the 
limits of 149/200 and 125/200, is withheld, a 
toxin is left free which is less virulent than that re- 
maining free between the limits of 124/200 and 
100/200 ; and from this point on the new unbound 
toxin may be still more virulent. The first would 
be tritotoxin, the second deuterotoxin and the 
third prototoxin. 

The "spectrum" of a toxin changes with its age. 
The prototoxin, and portions of the deutero- or 
tritotoxin may disappear because of toxoid forma- 
tion. Such changes have led to the recognition of 
an alpha and a beta modification of the toxin. 
The alpha modifications of all three toxins readily 
become toxoids. Only the beta modification of the 
deuterotoxin remains constant. The toxon also 
remains relatively intact (Figs. 2, 3 and 4). 

This very complicated method of investigation 
was also undertaken by Madsen in the study of 
tetanus toxin, for which a somewhat similar 
"spectrum" was constructed. 

Such spectra have not been worked out in de- 
tail for some of the vegetable toxins, as ricin and 
abrin, but it is known that they form toxoids. 

Some of the toxins of snake venom differ from 
the bacterial toxins in structure (pages 428-431). 
The Forma- The idea was originally advanced that antitoxin 
Antitoxin, is transformed toxin, a change in the latter hav- 
ing been effected through some action of the 
tissues. In that case, the amount of antitoxin pro- 
duced should be roughly equivalent to the amount 
of toxin injected. This, however, was found not 






SIDE -CHAIN THEORY. 



199 



to be the case. A single injection of tetanus toxin 
may yield 100,000 times the amount of antitoxin 
necessary to neutralize the toxin injected. An in- 
teresting experiment is on record which shows the 
fallacy of the view just mentioned. An animal, 
the serum of which was rich in antitoxins, was 
bled repeatedly until an amount of blood which 
equalled the total quantity normally present in the 
animal's body was drawn. Yet the antitoxic 
power of the new formed blood was practically un- 
changed. 

Metchnikoff, to explain this "overproduction" 
of antitoxin, has suggested that the toxin molecules 
may be taken up by phagocytic cells and broken up 
into an indefinite number of smaller molecules, 
each of which then is altered in some obscure man- 
ner so as to constitute a molecule of antitoxin. 

The views of Ehrlich have found wide accept- 
ance, and have provided a valuable working hy- 
pothesis for many investigations. A considera- 
tion of this subject introduces one at once to the 
well-known side-chain theory of immunity of 
Ehrlich. It may be considered briefly at this point, 
in so far as it involves the origin and nature of 
antitoxin. Ehrlich considers it fundamental, in 
regard to the metabolic activity of cells, to assume 
that the cell constituents must enter into chemical 
combination with food substances in order that the 
latter may be made available for the use of the 
cell. It is supposed that cells contain cer- 
tain atom groups of unknown chemical nature 
which make possible the binding of food sub- 
stances. The name of receptor was given to such 
groups, since substances are received into the cell 
through them. Inasmuch as the foods and some 



Elirlicli's 
"Side-Chain." 



Receptors. 



209 INFECTION AND IMMUNITY. 

Multiplicity other substances which penetrate the cells differ 
in their chemical nature, it is probable that there 
are various receptors for the various types of sub- 
stances. The binding, however, is but a prelimi- 
nary step to profound changes which the substance 
may next undergo, through the action of other, 
more vital, cell constituents. That is to say, the 
receptor is but a link to bring the substance into 
relationship with the vital activities of the cell, 
which Ehrlich supposes may reside in a hypotheti- 
cal "Leistungsikerri" (action center or nucleus). 
In view of this conception one readily understands 
the propriety of considering the receptor as a side- 
chain of the " Leistungshern" just as the chemist 
speaks of the various groups which may be at- 
tached to the benzol ring, or benzol nucleus, as 
side-chains (See Chapter XIX). 
Action of In preceding pages it has been emphasized that 
a toxin, in order that it may injure a cell, must 
enter into chemical combination with its constitu- 
ents, and it is a fundamental tenet of the Ehrlich 
theory that this union is one which takes place 
between the toxin and a cell receptor (side-chain). 
The cell receptor, then, either is a haptophore or 
possesses a haptophore as a part of its complex. 

As the physiologic demands are probably re- 
sponsible for the character of the various recep- 
tors, it is not likely that special receptors are 
created when some unusual substance, as a bac- 
terial toxin, is introduced into the body. Conse- 
quently, when toxin unites with a cell, it probably 
occupies receptors which, under normal circum- 
stances, are employed in some physiologic process. 
If some inert, non-toxic substance should com- 
bine extensively with cells, a corresponding num- 



RECEPTORS. 201 

ber of receptors, which ordinarily are used for 
normal metabolism, would be thrown out of func- 
tion. Union of this nature would be equivalent 
to an injury of the cell, and it is possible that the 
action of toxoids is of this mild nature. 




Fig. 5. — Graphic representation of receptors of the first 
order and of toxin uniting with the cell receptor, a, Cell 
receptor ; 6, toxin molecule ; c, haptophore of toxin mole- 
cule ; d, toxophore of toxin molecule ; e, haptophore of the 
cell receptor. From Ehrlich's "Schlussbetrachtungen," 
Nothnagel's System of Medicine, vol. viii. This cut is not 
to be taken as representing the actual morphology of toxins 
or cell receptors. Nothing is known of their morphology, 
if, indeed, they have any. The cut is intended merely to 
represent, in a graphic manner, the supposed chemical 
structure and mode of action of these substances. This 
statement applies also to Figures 6 and 7. 

When toxin unites with cells there is involved 
not only the diversion of cell receptors from their 
customary functions, but in addition the destruc- 
tive action of the toxin on the vital parts of the cell 






202 INFECTION AND IMMUNITY. 

(perhaps on the "Leistungskern"). The more 
toxin introduced, the greater the number of cell 
receptors bound, and the greater the injury to the 
cell. 
Hypothesis l n ca se a non-fatal amount of toxin has been 
bound, but sufficient to cause some injury, how 
does the cell respond to the injury? Weigert, a 
few years ago, gave expression to a hypothesis 
which is held to have some bearing on this ques- 
tion. In studying regeneration following injury 
he concluded that tissues have the tendency to 
reproduce not only to the extent of making good 
the injury, but that an excess of new tissue re- 
sults. The clearest example of this occurrence is 
that of scar formation, in which a seeming excess 
of new connective tissue cells is formed, 
which later disappears in part. Similarly, when 
a non-fatal amount of toxin unites with the 
overproduce receptors, a cell defect or injury is created. The 
side-chaJn°s! cell has for practical purposes lost so many recep- 
tors. This loss affects the vital activities of the 
cell, the "Leistungskem" and new receptors, iden- 
tical with those occupied, are reproduced. Follow- 
ing the law stated, they are reproduced in excess 
of the number injured, and the excess may be so 
great that the cell may be overfilled with them — 
so overfilled that many are discharged and reach 
the general circulation. These cast-off receptors, 
or side-chains, still retaining their power of unit- 
ing with toxin, constitute our antitoxins. As 
Behring has stated it, the receptor, when attached 
to the cell, is the agent through which the latter 
is attacked, but when cast off from the cell becomes 
its protector (Fig. 5). 



ANTITOXINS. 203 

As regards the structure of the antitoxin (cast- Receptors of 
off receptor), it is necessary to assume only the order. 
presence of the proper haptophorous group. Ehr- 
lich designates all receptors of this simple type as 
"receptors of the iirst order." In following 
sections we will have to do with receptors of the 
second and third orders. 

Wassermann gives the following list of anti- 
toxins : 

ANTITOXINS FOR BACTERIAL TOXINS. 

Diphtheria antitoxin. 

Tetanus antitoxin. 

Botulism antitoxin. 

Pyocyaneus antitoxin. 

Symptomatic anthrax antitoxin. 

Antileucocidin, an antitoxin for the leucocytic 

poison of the staphylococcus. 
Antitoxins for the blood dissolving toxins of a 

number of bacteria. 

ANTITOXINS FOR ANIMAL TOXINS. 

Antivenin for snake poison. 
Antitoxin for scorpion poison. 
Antitoxin for spider poison. 
Antitoxins for certain poisons of fish, eel serum, 
salamander, turtle, and for wasp poison. 

ANTITOXINS FOR PLANT TOXINS. 

Antiricin, for a red blood corpuscle poison of 

the castor oil bean. 
Antiabrin, for a similar poison of the jequirity 

bean. 
Antirobin, for robin, a locust tree poison. 
Anticrotin, for crotin, a toxin from the bean of 

Croton iiglium, the croton oil bean. 



204 INFECTION AXD IMMUNITY. 

Hay fever antitoxin, for the toxin of pollens 
which cause hay fever. 

ANTIPERMENTS. 

Antirennet. 

Antipepsin. 

Antitrypsin. 

Antinbrinferment. 

Antiurease, for urease, a urea splitting ferment. 

Antilaccase. 

Anti tyrosinase. 

Antisteapsin. 

Antiferments for the ferments of bacterial 
cultures. 

The above are true antitoxins. There are other 
substances, however, which occasionally exert an 
antagonistic action on toxins, although they prob- 
ably are not true antitoxins. For example, it has 
been found that cholesterin neutralizes the action 
of tetanolysin, the hemolytic toxin of the tetanus 
bacillus (Noguchi), and also the hemolytic action 
of cobra venom and cobra-lecithid. (See Chap. 
XVI). On the other hand, it does not affect two 
other hemolytic toxins, staphylolysin, which is 
derived from the staphylococcus, and arachuolysin 
which is obtained from spiders (Kyes), the action 
of cholesterin, therefore, is in no sense specific and 
apparently is of a different type from that of 
serum antitoxins. This is further indicated by 
the fact that chloesterin also inhibits the hemolytic 
activity of certain substances which can not be 
classed with the toxins, e. g. saponin, agaricin 
(Koguchi). Fluids which contain cholesterin nat- 
urally, as milk, serum and bile, have a similar 
inhibiting power. 



ANTITOXINS. 205 

The cliscovei\y of Hektoen that certain salts are 
able to neutralize the toxic action of some serums, 
by combining with the so-called complement, may 
also be mentioned in this connection. 



CHAPTER XIII. 



Specificity. 



Widal and 
Grunoaum. 



Normal 
Agglutinins. 



THE PHENOMENON OF AGGLUTINATION. 

Agglutination, in the bacteriologic sense, refers 
to the clumping and sedimentation of a homogene- 
ous suspension of micro-organisms by the action of 
a serum. 

Although a number of investigators had ob- 
served the phenomenon of agglutination, Gruber 
and Durham first saw its significance. They found 
that the reaction was a specific one, i. e., that the 
serum which would cause the strongest agglutina- 
tion of a micro-organism was that of an animal 
which had been made immune to it by repeated 
injections. 

Widal's service consisted in the utilization of the 
phenomenon as an aid in the diagnosis of typhoid 
fever. He is the originator of clinical serum 
diagnosis. It is perhaps largely a matter of acci- 
dent that we speak of the Widal reaction rather 
than the Griinbaum reaction. Griinbaum was car- 
rying on the same work at the same time, but 
Widal preceded him in the publication of his more 
extensive work. 

In the chapter on natural immunity it was 
stated that normal serums often are able to ag- 
glutinate bacteria. Normal human serum may ag- 
glutinate the typhoid, colon, pyocyaneus, and dys- 
entery bacilli, and occasionally the staphylococcus 
and cholera vibrio; it does not agglutinate the 
streptococcus and some other organisms. In cer- 
tain cases it may agglutinate" the typhoid bacillus 



IMMUNE AGGLUTININS. 



207 



even when the serum is diluted to one in thirty, a 
point of practical importance in the clinical use of 
the test. When a normal serum is found to have a 
high agglutinating power, a previous infection by 
the micro-organism is to be thought of. This pos- 
sibility receives emphasis from the fact that the 
serum of a new-born child is devoid of many of the 
agglutinins which are found in later life. Hence, 
of the so-called normal agglutinins, many, after 
all, may be acquired properties. 

The term immune agglutinin is applied to the 
agglutinating substance in a serum, when the 
property has developed as a result of infection, or 
of systematic immunization with the organism. 
Thoy are formed during infections with the organ- 
isms of typhoid, cholera, dysentery, plague, etc. 

For the artificial production of agglutinins, the 
bacteria may be injected into the veins, subcutane- 
ous tissue, or peritoneal cavity; in some cases they 
may be fed to animals, rubbed into the skin, or 
sprayed into the lungs. If certain micro-organ- 
isms are sealed up in a collodion sac and placed in 
the abdominal cavity of an animal, an agglutinat- 
ing serum will be formed ; the necessary substances 
diffuse through the sac and reach those body cells 
which produce the agglutinin. It is not necessary 
that living bacteria be injected ; in fact, the strong- 
est agglutinin is said to be formed by the injection 
of bacteria which have been killed by a tempera- 
ture of 62 C. In certain instances agglutinins are 
produced by immunization with disintegration 
products of bacteria or with bacterial extracts. 

Nearly all bacteria, even when non-pathogenic, 
will give rise to agglutinating serums when in- 
jected ; but not all have the power equally. Mcolle 



Immune 
Agglutinins, 



Agglntlnin- 

Prodncing: 

Organisms. 



20S INFECTION AND 1MMUXIT1. 

and Trenell distinguish three groups of bacteria 
in regard to their agglutinability by the homolo- 
gous antiserums. 1 The first group includes easily 
agglutinable organisms, for the most pathogenic: 
T} T phoid, dysentery, cholera, plague, glanders, and 
the colon, psittacosis, pyocyaneus bacilli, and B. 
enteritidis. They yield agglutinating serums read- 
ily either as a result of infection or by immuniza- 
tion. The second group comprises organisms 
which, during infection or convalescence, do not 
cause the formation of agglutinins, but may be 
forced to do so by systematically injecting them 
into animals. In the third group are included 
those which even during prolonged immunization 
rarely cause the formation of agglutinating 
serums: the Friedlander bacillus. These facts 
may be taken as an index of the diseases in which 
we may expect to obtain the agglutination reaction 
by the serum of the patient. 
variations in The degree of agglutinating power which may 
genie Power be obtained by immunization varies greatly. Van 
rgamsms. ^ er Velde speaks of a typhoid serum which in a 
dilution of one in one million was agglutinating, 
and Durham had a cholera serum which was ef- 
fective in a dilution of one in two millions. Such 
powerful serums are rarely obtained. 

Even two different strains of the same organism 
may differ in their ability to cause the formation 
of agglutinins. It is generally said that a typhoid 
strain, which is agglutinated with difficulty, gives 
rise to a weak agglutinating serum, while an easily 

]. The homologous organism for a typhoid serum, for ex- 
ample, is the typhoid bacillus, and vice versa ; other organ- 
isms, or other serums, are heterologous. These are commonly 
nsed terms. 



AGGLUTIXIXti. 



agglutinable strain gives a strong agglutinin. The 
logic of this will become apparent when we con- 
sider the nature of the bacterial substance which 
causes the body to produce agglutinin. 

That the agglutinating power of the serum of a 
typhoid patient varies from day to day is a fact 
of practical importance. It may be thirty times as 
strong one day as the next, and may even disap- 
pear entirely for a day or two. Hence the impor- 
tance of making more than one test in a suspicious 
case, when the first trial has been doubtful or 
negative. There is no adequate explanation for 
this great variation. It is said that mixed infec- 
tions, intestinal hemorrhage, or a sudden pouring 
out of typhoid bacilli into the circulation may 
cause a reduction in the agglutinating power. This 
occurrence has an important bearing on the possi- 
bility of using the agglutinating power of the 
serum as a prognostic sign. Although it has often 
been noted that in fatal infections agglutinins may 
be absent from the serum, the variations just men- 
tioned indicate that prognosis could not be based 
safely on the result of a single agglutination test. 

The agglutinating substance is found in the 
highest concentration in the -blood serum, but it 
may be demonstrated in the various body fluids 
and in extracts of the organs ; it is said to be par- 
ticularly rich in the milk. It is present in the 
serum of an artificially produced blister, and it has 
been recommended that blistering be resorted to 
in order to obtain serum for the test. The bile 
often agglutinates the typhoid bacillus, but the 
power has no necessary relationship to a pre-exist- 
ing infection ; it is possible that the agglutination 
in this case is due to obscure chemical causes 



Variations i 
Quantity of 
Agglutinins. 



Distribution 
of Agglutin- 
ins in Body. 



210 INFECTION AND IMMUNITY. 

rather than to the usual serum agglutinin. Becht 
and Greer find that agglutinins occur in the var- 
ious body fluids in the following order of concen- 
tration: blood serum, thoracic lymph, neck lymph, 
traces in the pericardial fluid, least and not con- 
stantly in the cerebrospinal fluid and aqueous 
humor. The administration of pilocarpin causes 
a rise in the agglutinating power of the tears, 
sputum and some other body fluids; the drug 
increases cell secretions. 
inheritance. When typhoid fever occurs during pregnancy, 
agglutinins may appear in the serum of the fetus. 
On the one hand it has been held that agglutinin 
passes from the mother to the fetus, or, on the 
other hand, that the presence of agglutinins arises 
from infection of the fetus itself. 

Although the milk may be very rich in agglu- 
tinin, it is doubtful if the serum of a breast-fed 
child undergoes much increase in its agglutinating 
power because of the ingestion of the milk. The 
intestinal juices (trypsin) digest agglutinins. 

The origin of agglutinins in the animal body is, 
according to very convincing experiments of 
Hektoen and Carlson, the tissue cells of the body. 
significance One of the most interesting and important phe- 
Sation". nomena in the study of immunity is the so-called 
Pfeiffer phenomenon. An animal which has been 
rendered immune to cholera by repeated injections 
of cholera vibrios has the power of digesting or dis- 
solving the latter when they are placed in the fresh 
serum or in the peritoneal cavity of the immunized 
animal. Gruber and Durham were studying this 
phenomenon in the test tube when they first ob- 
served the agglutination reaction. It was found 



AGGLUTINATION. 211 

that the agglutinating property, as well as the bac- 
tericidal power, was the result of immunization. 
Inasmuch as an increase in the bactericidal power 
of a serum points to the existence of an acquired 
immunity, the question naturally arises: Does the 
associated property of agglutination have a similar 
significance ? 

Many observations indicate that the two activi- 
ties are distinct, that they depend on different 
substances in the serum. The following are the 
important points involved : 

1. The bactericidal power is destroyed at 56 C. 
while agglutinins resist a temperature of 62 C. 

2. In certain cases it has been possible to cause 
the bacteria to absorb the agglutinin from the 
serum, leaving the bactericidal substance intact. 

3. A serum may be bactericidal, but not agglu- 
tinating. 

4. During the course of natural or experimental 
typhoid fever or cholera the development of the 
agglutinating and bactericidal powers may not be 
parallel. In cholera, the agglutinating power may 
disappear soon, but the bactericidal power remains 
for a long time. 

5. Micro-organisms which have been killed by a 
bactericidal serum may lose their toxicity; ag- 
glutinated bacteria remain virulent. 

Besredka found an apparent relationship be- 
tween agglutination and immunity; if typhoid 
bacilli were agglutinated before they were injected 
into the abdomen of a guinea-pig the animal would 
recover, but if they were not agglutinated death 
resulted. The explanation offered for this loss of 
virulence is that the bacilli being agglutinated and 
immobilized are more readily taken up by the 



INFECTION AXD IMMUNITY. 



Technic of 
the Aggluti- 
nation Test. 



The Bacterial 
Suspension. 



I 



phagocytes; if phagocytosis is inhibited by some 
means the agglutinated organisms are found to be 
still virulent. 

Koch has attempted to use the agglutination 
test with the tubercle bacillus as an index of im- 
munity against tuberculosis. This is not accepted 
as a reliable test for the immunity, but is perhaps 
a general index of the ability of the individual to 
form antibodies for this organism. This method 
was devised inasmuch as the bactericidal action of 
a serum on the tubercle bacillus is not readily de- 
termined. 

One may use two methods of determining the 
agglutination of bacteria : 1. the macroscopic or 
naked eye observation of the clumping and sedi- 
mentation of a homogeneous suspension of the 
bacteria in test-tubes; 2, the microscopic observa- 
tion of the clumping of the organisms when the 
latter are mixed with serum and mounted as a 
^langing-drop" preparation. 2 

When the organism to be tested grows rapidly, 
it is the custom to use a young culture, one which 
has grown on an agar surface or in bouillon for 
from eighteen to twenty-four hours. Older cul- 
tures of the tj'phoid bacillus or of the cholera 
vibrio are agglutinated with more difficulty than a 
young culture. If an agar culture is used, the 
bacteria may be washed from the surface by pour- 

2. For a hanging-drop preparation it is necessary to have 
a slide with a saucer-shaped depression on one surface. A 
drop of the solution to be examined is mounted on a cover 
glass, and the latter is then mounted, drop side down, over 
the depression and the edges of the cov^r-glass sealed with 
vaselin or paraffin. There is ample room for motile organ- 
isms to swim about in such a preparation, and the loss of 
motility incident to agglutination is readily observed. 



BACTERIAL SUSPENSION. 213 

ing 5 or 10 c.c. of physiologic salt solution into 
the tube and shaking vigorously; the resulting 
suspension is then ready for use. For either the 
macroscopic or microscopic test it is absolutely 
essential to have a homogeneous suspension of the 
bacteria, in order to avoid misinterpretations which 
may be occasioned by the accidental or natural 
bacilli were agglutinated before they were injected 
should be shaken thoroughly before the emulsions 
are used. This uniformity of suspension is readily 
accomplished with such organisms as the typhoid 
bacillus and cholera vibrio, motile organisms^ but 
when they grow in chains (streptococcus) or in 
coherent masses (diphtheria and tubercle bacilli) 
more violent measures must be resorted to. Daily 
shaking of a liquid culture of the diphtheria or 
tubercle bacillus is fairly effective, but the medium 
must be passed through a paper filter before it can 
be used safely; in this way the larger clumps are 
removed. Some investigators dry a large quantity 
of tubercle bacilli, grind them up thoroughly in an 
agate mortar and suspend the particles in salt 
solution; the fragmented condition of the organ- 
isms does not interfere with their participation in 
the reaction. One should have a uniform technic 
in preparing a bacterial emulsion in order to obtain 
as nearly as possible the same number of bacteria 
in a given volume of solution, on different occa- 
sions. For example, one may uniformly suspend 
a twenty-four-hour agar culture in 10 c.c. of salt 
solution. A uniform technic makes it possible to 
observe the quantitative relationship which exists 
between the mass of bacteria to be agglutinated 
and the agglutinating power of the serum. 



214 



INFECTION AND IMMUNITY. 



To Obtain 

Serum. 



Serum 
Dilutions. 



To obtain serum for the test one may resort to 
blistering: place a cantharides plaster from one- 
half to three-fourths of an inch square on the ab- 
dominal skin, protect it with a dressing, and in 
about twelve hours remove the serum with a steril- 
ized hypodermic syrirjge. Or, one may collect in a 
small test tube from 0.5 to 1 c.c. of blood from the 
lobe of the ear or finger-tip, and draw off the serum 
after it has separated by clotting. It is the cus- 
tom in some well-equipped laboratories to fill sev- 
eral U-shaped capillary tubes with blood from the 
lobe of the ear and to separate the blood from the 
serum at once by centrifugation. The custom of 
arying a few drops of blood on a coverglass or on 
filter paper, and of sending this preparation to a 
laboratory for the agglutination reaction, has been 
practiced quite extensively, and is a justifiable 
procedure when it is not possible to collect the pure 
serum. It has the disadvantage that the experi- 
menter never knows exactly how much blood has 
been collected, and consequently can not perform 
the test with exact dilutions of the serum, the im- 
portance of which will be pointed out below. The 
red corpuscles and debris in such a preparation also 
interfere with the clearness of the field in micro- 
scopic examination, a difficulty which may be 
partly overcome by filtering the dissolved serum. 

When only a small amount of serum is available, 
it is necessary to use the microscopic method. 
Normal human serum, when concentrated, and 
even when diluted to one in ten or higher, some- 
times agglutinates the typhoid bacillus and some 
other organisms; the same serum, when diluted to 
one in forty or one in sixty, may not agglutinate. 
The serum of a typhoid patient, however, or of a 



LOOP MEASUREMENT. 215 

t)'phoid convalescent rarely fails to agglutinate in 
these higher dilutions. It is generally held that 
a dilution of one in forty or fifty is sufficiently 
high to eliminate the possibility of agglutination 
by a non-typhoid serum, and sufficiently low to 
render the serums of all, or nearly all, typhoid pa- 
tients agglutinating. The necessity for dilution of 
the serum is emphasized by the additional fact 
that infections with related organisms, as the colon 
bacillus, cause a slight increase in the agglutinat- 
ing power for the typhoid bacillus along with a 
relatively large increase of colon agglutinins. A 
test with a low dilution of this colon serum might 
give a positive reaction with the typhoid bacillus 
and lead to an incorrect interpretation; but 
if a dilution of one in forty were useci, the non- 
agglutination of the typhoid bacillus would speak 
against a typhoid infection. This will be consid- 
ered under "group agglutination" (Chapter XIV). 

A convenient method of measuring small The "Loop" 

. - -,. t . ■, » Measurement. 

amounts of culture and serum is by means of a 
fine platinum wire which is bent at its tip to form 
an eyelet or "loop." 3 If one places one loop of 
serum into a small watch glass or hollow-ground 
slide, and adds nine loops of bouillon or of salt 
solution, a dilution of one in ten is reached. Five 
loops of this mixture with five of the diluent gives 
a dilution of one in twenty. One loop of the sec- 
ond dilution, to which is added one of the culture 
suspension, gives the desired dilution of one in 
forty. The last may be mixed directly on the 
coverglass, and then inverted on a hollow-ground 

3. Pfelffier introduced a conventional "loop" of such 
dimensions that it holds 2 milligrams of bacterial cells as 
they are taken from a solid surface, like that of agar. 



216 INFECTION AXD IMMUNITY. 

slide. More accurate dilutions can be made by 
means of capillary tubes. 

A convenient amount of serum is allowed to 
enter the tube by capillary attraction. The length 
of this column is marked on the tube and then 
successive volumes of the diluent drawn in, each 
being separated from the succeeding one by a small 
bubble of air. It is readily seen how with even a 
minute quantity of serum, one may make the test 
with dilutions of one in ten, one in twenty, one in 
thirty, one in forty, etc., details which are neces- 
sary for a correctly performed test. It is im- 
portant that in the different dilutions the same 
amount of bacterial emulsion be used. 

In the macroscopic test, more serum is neces- 
sary, though the quantity need not be large, and 
the dilutions are made in test tubes of suitable 
size. One should always deal with definite quan- 
tities of the serum dilutions, and should always 
add the same amount of bacterial emulsion in the 
various tubes involved in a test. 
The Micro- If agglutination occurs in the microscopic prep- 
Reaction, aration described above, one sees, with the high 
power, in the course of from fifteen minutes to a 
half-hour, that two or more micro-organisms 
which come in contact have a tendency to remain 
in this position. In the case of a motile organism 
(typhoid) the movements may be exaggerated for 
a time. In the course of the next few hours, other 
cells are added to incipient groups and new groups 
originate. Motility becomes less and less and event- 
ually ceases, in a characteristic reaction. The 
maximum change has taken place in from six to 
eiorht hours. jSTot less than four or five cells which 



AGGLUTININ UNIT. 217 

are permanently agglutinated are considered in- 
dicative of a positive reaction; the test is most 
decisive when large masses are formed, so large that 
they are seen readily with a low magnification. A 
similar preparation to which no serum has been 
added should always be made, in order to eliminate 
spontaneous or "auto-agglutination" as a possible 
source of error. 

In a macroscopic test, the uniform cloudiness of me Macro- 
the mixture of serum and bacteria becomes JSSJetion. 
changed by the formation of smaller and larger 
flakes or clumps of bacteria, which in the course of 
a few hours sink to the bottom as a white precipi- 
tate, leaving a clear overlying fluid. Here also a 
control tube, to which no serum has been added, 
should be preserved for comparison. 

The body temperature, which may be obtained 
in a thermostat, facilitates the reaction. 

The value of an agglutinating serum can not be Tlie As -giiiti- 
expressed in units with the exactness that is at- l,in Unlt - 
tained in measuring diphtheria antitoxin for the 
following reasons : 1, The limits of the reaction are 
not sufficiently definite ; 2, a given mass of bacteria 
has the power of absorbing varying amounts of 
the agglutinating substance, depending on the con- 
centration of the latter; and 3, it is impossible to 
obtain standard bacterial emulsions. 

One may arbitrarily decide on a unit similar to 
that of Ztipnik, in which a serum which is able 
to agglutinate a given mass of bacteria in a dilu- 
tion of one in forty is taken as the standard. If a 
similar amount of a serum agglutinates in a di- 
lution of 1 in 120 it is said to be of threefold 
strength. 



21S 



INFECTION AND IMMUNITY. 



A ft glut inatioii 
of Red Blood 



The value of the agglutination reaction as a 
clinical diagnostic aid will be considered later in 
connection with the individual diseases. 

A consideration of agglutination would be in- 
corpuscies. complete if one did not mention the phenomenon 
as it occurs with cells other than those of bacteria, 
in particular the red blood cells. The serums of 
many animals, as stated in a previous chapter, are 
toxic for the erythrocytes of some other species. 
In some instances, the corpuscles lose their hemo- 
globin under the influence of the serum (hemoly- 
sis) ; in other instances, or even with the same 
serums if previously heated, the corpuscles are 
thrown into clumps and settle to the bottom of the 
test tube, leaving a clear overlying fluid. The 
analogy with the bacterial agglutinins goes still 
further, in view of the fact that the formation of 
these '^hemagglutinins" may be induced artificially 
in the body of an animal by the injection of 
erythrocytes from another species. An animal 
does not form agglutinins for its own cells (auto- 
agglutinins), but often does, however, for the cells 
of another member of the same species (iso-agglu- 
tinins). What is said in the next chapter con- 
cerning the specificity of the bacterial agglutinins 
also holds for the hemagglutinins. 

Certain plant toxins, true toxins with hapto- 
phorous and toxophorous structures, agglutinate 
red blood cells: ricin, abrin, crotin, etc. Some of 
the earliest and most important work which 
Ehrlich has done in the field of immunity was ac- 
complished with these plant toxins. 



Plant Hemag- 
glutinins. 



CHAPTER XIV 



THE NATURE OF THE SUBSTANCES CONCERNED IN 
AGGLUTINATION. 

Two substances are concerned in agglutination : Terms. 
one, the active or agglutinating substance, exists 
in the serum, while the other, the substance acted 
on or the agglutinable substance, is present in the 
bacteria. The agglutinable substance is generally 
supposed to be passive in the reaction, while the 
agglutinating property seems to possess a ferment- 
like element, which acts on the agglutinable sub- 
stance. Agglutinin, the term used in the preced- 
ing chapter, is now generally applied to the sub- 
stance in the serum. Recently the bacterial con- 
stituent has been called agglutinogen, because of 
the belief that the agglutinable substance, when 
introduced into the animal body, stimulates the 
latter to the formation of agglutinin; hence ag- 
glutinogen means, not agglutination-producing, 
but agglutinin-producing. These shorter terms 
will be used for the sake of convenience. 

The presence of agglutinogen in an organism Agglutinogen. 
may be demonstrated in three ways : 1. The mere 
fact of its agglutinability by a serum is evidence 
of the presence of an agglutinable substance. 2. 
If during infection or immunization the serum ac- 
quires agglutinating properties, the bacterium pos- 
sesses an agglutinogenic substance. 3. If a cul- 
ture is mixed with a serum containing the specific 
agglutinin, and after a period of contact is re- 
moved by centrifugation, the resultant disappear- 



220 INFECTION AND IMMUNITY. 

ance of agglutinin from the serum, which may be 
demonstrated, shows that something in the bac- 
teria (agglutinogen) has combined with the ag- 
glutinin. 

Distribution The location of agglutinogen in the bacterial 
nog-en" cells has received some discussion. There is a tend- 
ency to believe that it exists in the cell envelope or 
perhaps on its surface. It appears to be formed in 
the cell, and, in some cases, it may be excreted into 
a surrounding medium; certainly when bacteria 
die and disintegrate agglutinogen is liberated. The 
filtrates of certain cultures (entirely free from 
bacterial cells), when injected into animals, will 

Also, just as 
•glutinin from 
the corresponding antiserum by a process of 
chemical union, so a filtrate of the type mentioned 
is able to neutralize the agglutinating power of the 
serum. In these instances, agglutinogen becomes 
free as a consequence of disintegration of some of 
the bacterial cells. 

The Precipi- The filtrates of certain cultures exhibit another 
Reaction phenomenon when they are mixed with their spe- 
cific antiserums; this has to do with the bacterial 
precipitins of Kraus. If, for example, the filtrate 
of an old typhoid bouillon culture is mixed with 
antityphoid serum, a distinct precipitate is formed 
which eventually settles to the bottom of the tube. 
This is a specific reaction, and does not occur if the 
filtrate is mixed with some other immune serum. 
It is thought by some that this so-called precipi- 
table substance in the filtrate is identical with the 
agglutinable substance (agglutinogen), but this 
point is still the subject of investigation. 



AGGLUTINOGEN. 



221 



Multiplicity 
of Agglutino- 
gens. 



Agglutinogen may be extracted from micro- 
organisms by chemical processes. The presence 
of the substance in the extracts becomes manifest 
when immunization with them causes the forma- 
tion of an agglutinating serum. This, again, is 
the "test of immunization." 

The agglutinogen of one bacterium is not iden- 
tical with that of any other. If they were identi- 
cal, immunization with the one would yield an ag- 
glutinating serum of equal power for both cells; 
this, however, is not the result obtained. On the 
other hand, the agglutinins of two different organ- 
isms may coincide to a certain degree, as will be 
shown under the subject of "group agglutination." 
Certain experiments go to show that the agglutin- 
ogen of even a single micro-organism is not uni- 
form substance. One portion is heat-susceptible, 
being destroyed at 62 C, while another portion is 
said to resist a temperature of 165 C. Such tech- 
nical questions continue to be investigated. 

Agglutinogens are said to pass through semi- Flagellar and 

-it -u I.*! - i j.- • j j. Somatic Ag- 

permeable membranes, while agglutinins do not. giutinogens. 

Smith and Reagh distinguish two kinds of ag- 
glutinogen in those bacteria which possess flagella, 
one peculiar to the cell body, and the other to the 
flagellar 

Agglutinin may be precipitated completely from 
a serum by the sulphates of magnesium or ammo- 
nium, when the salts are used in proper concentra- 
tions. Because of their reaction to such precipi- 
tating agents, agglutinins are thought to belong to 
the globulin fraction of serums ; whether globulins 
or not, they are precipitated with them. 

Agglutinins resist digestion with pepsin and 
papayotin, but are destroyed after prolonged ex- 



Properties of 
Agglutinins. 



INFECTION AND IMMUNITY. 



Structure of 
Agglutinogen. 



posure to the action of trypsin. An agglutinating 
serum which is dried and kept free from moisture 
and the action of light retains its power unaltered. 
Similar to agglutinogen, agglutinin is thought not 
to be a uniform substance, one portion being sus- 
ceptible to heat, and another portion resistant; 
these have been called alpha and beta agglutinins. 
It is convenient to speak of the reaction between 
agglutinin and agglutinogen, and of the process in 
the body through which agglutinins are formed, in 
terms of the side-chain theory. Accordingly, if 
that constituent of micro-organisms which we have 
termed agglutinogen is the substance which stimu- 
lates the tissues to form agglutinin, we must as- 
sign to it a haptophorous group through which it 
may unite with the receptors of the tissue cells. 
This haptophore comes into play again in the union 
between agglutinogen and agglutinin, which pre- 
cedes agglutination. There is no reason for as- 
signing to agglutinogen any other structure than 
this single haptophore ; it is a passive body, similar 
to antitoxin, and has no other function than that 
of uniting either with cell or with agglutinin. 

Agglutinin also must have a haptophorous or 
binding group, inasmuch as it enters into combina- 
tion with agglutinogen. In addition to this bind- 
ing group, experiments have shown that agglutinin 
possesses a toxic constituent, which is analogous 
to the toxophorous group of the toxin molecule. 
In this case, however, it is called a zymotoxic, 
zymophorous or agglutinophorous group; suppos- 
Gronp. e $iy it has a ferment-like activity (Fig. 6). The 
analogy with toxins goes further, in that the 
zymotoxic group of agglutinin may degenerate or 
may be destroyed, leaving the haptophorous group 



Structure of 
Agglutinin. 



Zymotoxic 



AGGLUTINOIDS. 




with its binding power for agglutinogen practi- Assiutinoids. 
cally unaltered; these are agglutinoids, just as 
toxins when changed in a similar way are called 
toxoids. A serum which is rich in agglutinin may 
be changed into one rich in agglutinoid by expo- 
sure to a temperature of from 60 to 75 C, and by 
the action of acids or alkalies; the change also 
takes place spontaneously in the course of time, 
when the agglutinin is in solution. 

Agglutinoids are detected by methods analogous 
to those used in the recognition of toxoids. If 
toxoids unite with all the antitoxin in a solution, 
there naturally remains no antitoxin to unite with 
true toxin which may be added subsequently. Sim- 
ilarly, if all the agglutinogen in a mass of micro- 
organisms has united with inactive agglutinoid, 
agglutinin which is added subsequently would have 
no point of attack and the reaction of agglutina- 
tion would not occur. So we may say that when 
bacteria are treated with a serum which has lost 
its original agglutinating power, and the bacteria 
are thereby made insusceptible to the action of a 
fresh agglutinating serum, the former serum con- 
tains agglutinoids. 

Sometimes it is found that even a fresh serum, 
when concentrated, will cause less agglutination 
than when diluted. This has been referred to the 
presence of agglutinoids which have a stronger 
affinity for agglutinogen than has the agglutinin; 
when of this character they are called proagglu- 
tinoids, and accordingly are analogous to the pro- 
toxoids mentioned earlier. As the serum is diluted 
the concentration of the pro-agglutinoids becomes 
less, and at a time when they are so dilute that they 
have no influence on the reaction, the agglutinins 



Proag- 
glutinoids. 



224 



1XFECTI0X AXD IMMUX1TY. 



Two Stages in 
Agglutina- 
tion. 



Gronp Ag- 
glutination. 



are still present in such quantity that agglutina- 
tion is brought about. 

The presence of some salt is necessary for the 
occurrence of agglutination. Bordet found that 
if the salts were removed from the serum and from 
the suspension of bacteria by dialysis, and the two 
were then mixed, agglutination did not occur; if 
a small trace of sodium chlorid was added the re- 
action took place promptly. Furthermore, if the 
serum was completely removed from the bacteria 
by repeatedly washing them in distilled water, it 
was found that the microbes had absorbed the ag- 
glutinin, but the latter remained inactive until the 
salt was added. 

This experiment not only suggests a haptophor- 
ous as distinguished from a zymotoxic group, but 
also indicates that agglutination consists of two 
phases. The first phase represents the union of 
agglutinin with the bacteria, while in the second 
are included the other changes necessary for the 
clumping of the organisms, in which the activity 
of the zymotoxic group is represented. The action 
of the salt, just cited, is unknown. 

The properties of serums which are of interest 
in immunity are now being studied by chemists, 
notably by Arrhenius. The study of mass action, 
of chemical equilibrium between agglutinin and 
agglutinogen, for example, and of the dissociation 
of the compound after it has once formed, are 
subjects under investigation, but which are too 
technical to be entered on here. 

"Group agglutination" has been referred to. By 
this is meant the ability of an antimicrobic serum 
to agglutinate certain other organisms which mor- 
phologically, biologically and often pathogeneti- 






GROUP AGGLUTINATION. 225 

cally, are closely related to the homologous bac- 
terium. In these instances, the agglutinating 
power is greatest for the homologous organism, 
and the degree to which the heterologous organisms 
are agglutinated is, to some extent, an index of 
the proximity of the relationship of the latter to 
the former. Antityphoid serum has been found to 
agglutinate the psittacosis, colon, paracolon, and 
paratyphoid bacilli and Bacillus enteritidis, but 
the action is never so strong as on the typhoid 
bacillus itself. We are to understand that this 
power to agglutinate related organisms represents 
something more than the normal property of the 
serum; there has been an actual increase in agglu- 
tinin for the heterologous bacteria as a result of 
infection or immunization by the primary organ- 
ism. 

Having typhoid fever in mind, this is a rule 
which works both ways. Infections with the colon 
bacillus and related organisms, and sometimes 
with organisms not closely related, as the staphylo- 
coccus, may cause an increase in agglutinin for the 
t}rphoid bacillus. The importance of this fact is 
evident, and it may explain the positive Gruber- 
Widal reaction sometimes found in infections 
other than typhoid. 

Inasmuch as the highest agglutinating power is ciiief Agrsrin- 

i .« I • , ,i -i i . tinin and Co- 

always mamtest against the homologous organism, Assintinin. 
this is spoken of as the chief agglutinin (Haupf- 
agglutinin) of the serum, while the weaker agglu- 
tinins for other organisms are called partial or ad- 
ventitious agglutinins, or coagglutinins (Mitag- 
glutinin). 

The phenomenon of group agglutination would s i> ecifici *y- 
seem to violate the specificity which we are in the 



226 INFECTION AND IMMUNITY. 

habit of attributing to the reactions of immunity; 
yet a reasonable explanation has been offered for 
the occurrence. It is probable that the proto- 
plasms of all cells have certain constituents in 
common, and that the closer the relationship be- 
tween two different cells the greater is the simi- 
larity of their constituents. In view of this prob- 
ability, Durham has used the following illustra- 
tion in the explanation of group agglutinations : 
The typhoid bacillus contains certain constituents, 
agglutinogenic molecules, which one may desig- 
nate as a, b, c, d, and e ; these differ among them- 
selves in unknown respects, but each is able to 
stimulate to the formation of a corresponding ag- 
glutinin. The serum, then, would have the ag- 
glutinin molecules A, B, C, D and E, also differing 
among themselves, but having at least one property 
in common — that of causing agglutination of the 
typhoid bacillus by uniting with the correspond- 
ing agglutinogenic molecules. In this sense noth- 
ing could be more specific. The Bacillus enteri- 
tidis, closely related to the typhoid organism, may 
possess the agglutinogenic molecules c, d, e, f, g, 
and h, and following the principle expressed above 
would stimulate, in the body, to the formation of 
the agglutinin molecules C, D, E, F, G and H. 
Inasmuch as the agglutinogens c, d and e are com- 
mon to the two bacilli, the agglutinins C, D and E, 
which are present in both serums, would affect 
pither of the two organisms. The typhoid serum, 
however, would contain five agglutinins for the 
typhoid bacillus and only three for the Bacillus 
enteritidis, consequently the action would be 
stronger against the typhoid bacillus ; mutato mu- 
tandis, the samo applies to the enteritidis serum 



SPECIFICITY OF SERUM. 227 

The same line of reasoning would explain the in- 
creased agglutinating power of an anticolon serum 
for the typhoid bacillus. 

A further elaboration of this principle may be 
made in a case in which two different strains of 
the same organism (typhoid bacillus) have some- 
what different agglutinogenic molecules; conse- 
quently the homologous immune serums for the 
two organisms might not coincide in their ag- 
glutinating powers for a third strain of the bacil- 
lus. 

In view of the points mentioned, it is clear that gJJJ^ tance of 
specificity of a given serum may be determined 
only by diluting the serum to such an extent that 
the coagglutinins practically are eliminated, the 
chief agglutinin being present in so much greater 
concentration that it is still able to agglutinate 
the homologous bacterium. 

Theoretically, it is also important for the spe- 
cificity of the reaction that the particular strain 
of the organism to be used for the test correspond 
in its agglutinogenic molecules or receptors with 
those of the strain used for the immunization ; the 
agglutinogenic receptors should be typical for the 
organism. 

It is doubtful if group agglutination occurs 
among all closely related bacteria, inasmuch as 
Kolle found that it did not exist among the vib- 
rios. 

It is thought possible that the multiple agglu- Dilutions. 
tinating power of a serum may be caused by mixed infections. 
infections in some instances. Although this is to 
be kept in mind, one should not overestimate its 
diagnostic importance, because a similar multi- 



228 



INFECTION AXD IMMUNITY. 



Production 
of Agglu- 
tinins. 
Ehrlich 
Theory. 



Second 
Order. 



plicity may result from infection by a single micro- 
organism. 

The explanation of the production of aggluti- 
nins by the bod} r , according to the conception of 
Ehrlich, is similar to that already given 'for the 
production of antitoxins. That is to say, the ag- 
glutinin molecules are cast-off cell receptors, the 
overproduction of which has occurred as a result of 
their union with the agglutinogen^ molecules of 
the bacteria. The antitoxin receptors were rela- 
tively simple, having no other demonstrable struc- 
ture than that of the haptophorous groups through 
which they unite with the corresponding toxin. 
We have recognized in the agglutinin receptor two 
groups, a haptophorous and a zymotoxic; conse- 
quently it must have this same structure when it 
is still a part of the cell. Ehrlich designates it as 
a receptor of the second order, which, being de- 
fined, is a receptor in which a haptophorous and a 
zymotoxic group exist as integral parts of the 
molecule (Fig. 6). 

In accordance with the side-chain theory, the 
ability of an animal to form agglutinins for a cer- 
tain organism would depend on its possession of re- 
ceptors of the second order which are able to unite 
with the agglutinogen^ receptors of the bacterium. 
It is well established that different animals may 
not form serums with equal agglutinating powers 
for an organism. The following is a concrete ex- 
ample: Wassermann immunized rabbits, guinea- 
pigs and pigeons with a strain of the colon bacil- 
lus, and tested the three serums with fifteen other 
strains of the same organism. The serum of the 
guinea-pigs readily agglutinated the strain which 
was used for immunization, but scarcely affected 



SPECIFICITY OF SERUM. 229 

the others. The serums of the rabbits and pigeons 
also agglutinated the homologous culture, but the 
coaggiutinins which they possessed did not affect 
other strains equally. Consequently, it was sup- 
posed that the cells of the three animals contained 
a limited number of receptors in common, whereas 




Fig. 6.- — Graphic representation of receptors of the second 
order and of some substance uniting with one of them, c, 
cell receptor of the second order ; d, toxophore or zymophor- 
ous group of the receptor ; e, haptophore of the receptor ; f, 
food substance or product of bacterial disintegration uniting 
with the haptophore of the cell receptor. From Ehrlich's 
"Schlussbetrachtungen," Nothnagel's System of Medicine, 
vol. viii. 

other receptors which were present in one of the 
animals were largely wanting in the other two. 

Inagglutinability was mentioned as a charac- Aggiutinabii- 
teristic of certain bacteria, especially the bacillus oi^2nisS^. e 
of Friedlander. This condition is much more 
important when it involves an organism which 



230 INFECTION AXD IMMUNITY. 

usually is agglutinated with ease. In some in- 
stances, the typhoid bacillus when freshly culti- 
vated from a patient, or, indeed, from contami- 
nated water, has been found to resist agglutination 
by a strong serum; the same organism after a 
period of existence on artificial media becomes ag- 
glutinable. Widal and Sicard noted that often the 
serum of a typhoid patient would not agglutinate 
the bacillus which had been cultivated from the 
patient's own body, although the same serum 
would agglutinate laboratory cultures. Cultiva- 
tion of the typhoid bacillus at 42 C. will cause it 
to lose its agglutinable property, but it may be re- 
established by subsequent cultivation at lower 
temperatures. It seems that this variation must 
be due to some change in the bacteria, i. e., in the 
agglutinable substance. It is possible that the 
organism, during its existence in the animal, be- 
comes immunized against the action of the agglu- 
tinin just as the animal becomes immunized 
against the toxic action of bacteria. This condi- 
tion in the micro-organisms would then be repre- 
sented by a great excess of agglutinogen^ recep- 
tors, so that a much greater amount of agglutinin 
would be required to cause clumping. It is read- 
ily seen how the use of an inagglutinable strain of 
the typhoid bacillus would affect serum diagnosis. 
Theories* of We are to consider that in the phenomenon of 
tion. agglutination a reaction of a chemical or physico- 
chemical nature takes place between the agglutinin 
of the serum and the agglutinogen of the micro- 
organisms, the actual clumping following as a 
consequence of this reaction. It is not a "vital" 
reaction, for dead bacteria may be agglutinated. 



AGGLUTINATION. 231 

Theories of agglutination have to do, not with 
the existence of agglutinin and agglutinogen, but 
rather with the nature of the reaction between the 
two, and the influences which bring about the 
clumping after the reaction has occurred. The 
original theory of Gruber supposed that the serum 
so affected the bacteria that they became sticky; 
consequently, as they came in contact, they were, 
so to say, glued together. Dineur thought changes 
occurred in the flagellar of the organisms, a theory 
which is untenable because some bacteria are ag- 
glutinable which do not possess flagellar Em- 
merich and Loew refer agglutination to the action 
of an enzyme which is produced by the bacterium 
itself, a theory which is not given general credence. 
Bordet excludes the vitality or motility of the or- 
ganisms as factors, and believes that the process is 
purely a physical one, because of the fact that 
some known chemical substances may be made to 
precipitate or to agglutinate certain other sub- 
stances (precipitation of colloids by salts) ; the 
theory presupposes some change in the molecular 
attraction between the microbes and the surround- 
ing fluid. 

Other theories have to do with the question of 
precipitation. As previously stated, when the fil- 
trates of cultures of certain organisms are mixed 
with their corresponding immune serums, precipi- 
tates occur in the mixtures. It was mentioned 
that the substance in the filtrate which takes part 
in the precipitation may represent, in part, the ag- 
glu tin able substance which has been excreted by 
the bacteria. Mcolle supposes that the agglutin- 
able substance resides in the external layer of the 
bacteria and that when the serum is added a coag- 



232 INFECTION AXD IMMUNITY. 

ulation occurs in 'the envelope, rendering coales- 
cence with the envelopes of other individuals pos- 
sible. The theory of Paltauf that the agglutinable 
substance finds its way to the surface of the bac- 
terium and is precipitated by its union with ag- 
glutinin is somewhat similar. The shell of the co- 
agulated substance accounts for the sticky charac- 
ter which the envelope acquires, according to the 
theory of Gruber. Paltauf cites observations 
which tend to show that some substance actually 
is extruded from the micro-organisms during ag- 
glutination, and that in properly stained speci- 
mens it can be seen as a precipitate surrounding 
and between adjacent organisms. 

The multiplicity of theories leads one to suspect 
that the true nature of the process remains obscure. 
The physical nature of the reaction is strongly 
supported by the facts that bacteria may also be 
agglutinated and precipitated by well-known chem- 
ical substances, such as hydrochloric acid, and by 
various organic and inorganic colloids (colloidal 
solutions of calcium chlorid (CaCl 2 ), zinc sulphate 
(ZuSoJ, ferric hydroxid (Fe(OH) 3 ), aluminum 
hydroxid (Al(OH) 3 ), ferric chlorid" (Fed,) and 
aluminum chlorid (A1C1 3 ). Some of these sub- 
stances behave like the agglutinating serums in 
the possession of the so-called prozone; i. e., they 
may fail to agglutinate in more concentrated solu- 
tions, whereas after dilution, their agglutinating 
power becomes manifest (hydrochloric acid and the 
staphylococcus, according to Buxton and Rahe). 
Still further indirect evidence of this nature of 
the reaction is found in the observation, made first 
by Neisser and Friedberger, that two colloids which 



AGGLUTIXATIOX. 233 

bear opposite electrical charges result in sedimenta- 
tion when they are mixed in suitable proportions. 
Eosin and Bismarck brown, mastic and colloidal 
ferric hydroxid (Fe(OH) 3 ), colloidal silicic acid 
and colloidal ferric hydroxid are mixtures which 
behave in this way. Here also the inhibiting 
"prozone" is obtained in concentrated solutions. 

An analogy appears to exist between bacteria 
which have absorbed agglutinin and certain colloids 
in that both may be agglutinated by the addition 
of suitable electrolytes. This phase of the agglu- 
tination of bacteria was referred to previously. In 
a like manner "agglutinin-bacteria" and the col- 
loids mentioned may alike be precipitated by 
various salts (electrolytes), such as the chlorids of 
sodium, calcium and potassium, and many others. 1 

1. Buxton and Rahe : Jour. Med. Research, 1909, xx, 113. 



CHAPTER XV. 



Precipitins. 



PRECIPITINS. 

Because of their scientific importance and cer- 
tain practical features, the serum-precipitins 
should receive something more than the incidental 
mention which has been given them under agglu- 
tination and in other chapters. 
Bacterial In 1897 Kraus discovered that bouillon cultures 
of the organisms of typhoid, cholera and plague, 
from which the bacteria had been removed by fil- 
tration, would cause precipitates when mixed with 
their respective antiserums. The reaction is spe- 
cific. As stated later, however, this specificity 
holds only when those quantitative relationships 
are observed which were found so essential for the 
agglutination test. The precipitins of Kraus are 
the bacterial precipitins. He proposed their use 
for the identification of micro-organisms. If, for 
example, one has in hand a culture which he sus- 
pects to be that of the typhoid bacillus, it may be 
grown in a liquid medium, the cells removed by 
filtration, and the filtrate mixed with a known 
antityphoid serum; if a precipitate occurs when 
the serum is sufficiently diluted, the reaction indi- 
cates that the organism in question is the typhoid 
bacillus. Inasmuch as precipitins are formed dur- 
ing the course of some infections it may be possible 
to use them in clinical diagnosis, but for either 
bacterial or clinical diagnosis the agglutination 
test is more readily performed and interpreted. 



PRECIPITINS. 



235 



Phytoprecipitins are produced by immuniza- Phytoprecipf- 
tion with albuminous substances of plant origin, zooprecip- 
as ricin and albumin from grains, and their action ltins - 
is specific for the homologous substance. 

Zooprecipitins are obtained by immunizing with 
animal albumins. Through the work of Wasser- 
mann and Uhlenhuth, of Nuttall, and others, it 
has been demonstrated as a general law that im- 
munization with an albumin from whatsoever 
source gives rise to the formation of a precipitin 
which manifests its action only against the par- 
ticular albumin used for the immunization. Hence, 
the albumin of a particular serum, in some un- 
known respect, is different from that of all others ; 
it is special to the species. 

Immunization with milk causes the formation Lactosemm. 
of a precipitin which throws down the casein of 
the milk used for injection, but not that of milk 
from another species. The milk of the goat may 
be differentiated from that of the cow by the use 
of the lactoserum. 

Likewise, after the injection of egg-white a 
precipitin is formed which is specific for the type 
injected. 

Three substances are open to study in the pre- 
cipitation reaction. First, the fluid or substance 
which is used for immunization ; it bears the name 
of precipitogen, i. e., the precipitin-producing sub- 
stance, Second, the specific constituent of the 
precipitating serum, i. e., the precipitin. Third, 
the precipitate, which is a consequence of the reac- 
tion between precipitogen and precipitin. We are 
able to recognize in this instance the actual end- 
product of a reaction, a condition which is not so 
easily realized in other "immunity reactions." It 



Precipitogen, 
Precipitin 
and Precipi- 
tate. 



reci pit in. 






23G INFECTION AND IMMUNITY. 

is true, of course, that little has been learned con- 
cerning the nature of the end-product; its chemis- 
try is as dark as that of the proteids in general. 
Formation of As stated in the chapter on "Natural Immun- 
ity," normal serums occasionally have the power 
to cause precipitates in other serums. Precipitins 
for egg albumin and goat serum have been found 
in extracts of organs, although at the same time 
they were absent from the serum of the animal. 
In this case the active bodies exist in the cells as 
"sessile receptors," and by the process of extraction 
they are brought into solution. During immuniza- 
tion these same receptors are stimulated to over- 
production and are thrown into the circulation as 
free precipitin receptors. 

The power of forming precipitins may be widely 
distributed among the organs. This function has 
been assigned to the leucocytes (Kraus and Leva- 
diti, Moll), and in one case they were formed 
locally in the anterior chamber of the eye (v. 
Dungern, Romer). 

For the artificial production of precipitins the 
precipitinogenous fluid may be injected into the 
veins, peritoneal cavity or the subcutaneous tissue. 
Within from four and a half to five days the pre- 
cipitin has been formed to such an extent that it 
may be demonstrated in the serum of the im- 
munized animal. 
concerning: As in the case of agglutinin formation, not all 
animals have equally the power of forming a pre- 
cipitin for a given albumin. This point, as re- 
lated to serum precipitins, is of particular impor- 
tance, and involves a factor which is of no conse- 
quence in bacterial agglutinins. In the first 
place, an animal will not form a precipitin which 



An to precipi- 
tins a n«l Iso- 
preeipitins. 



PRECIPITINS. 



237 



is active against its own serum, i. e., by bleeding 
an animal and reinjecting the serum a specific pre- 
cipitin is not formed. If formed it would be an 
autoprecipitin, and, as a rule, animals do not form 
antibodies for their own tissue constituents. 
Again, animals are less likely to form antibodies 
for the tissue constituents of other members of the 
same species than for those of other species ; these, 
when formed, are called iso-antibodies. Schutze 
immunized thirty-two rabbits with serum from the 
rabbit and obtained an iso-precipitin from only two 
of the number. In the third place, animals do not 
readily form anti-bodies for the tissue constituents 
of other animals which zoologically or biologically 
are closely related. Immunization of the guinea- 
pig Avith the serum of the rabbit, a pigeon with 
that of a chicken, or a monkey with human serum, 
are procedures which usually do not yield precipi- 
tating serums. 

Chemically, little is known of precipitins. They 
are thrown down by ammonium sulphate in con- 
junction with the euglobulin fraction of serum, and 
are destroyed by those substances which alter al- 
buminous bodies, as acids, alkalies, pepsin and 
trypsin. That bacterial precipitins are not iden- 
tical with agglutinins for the same bacteria is 
shown by the following facts : Immunization with 
certain bacteria may produce agglutinin but no 
precipitins. Precipitins develop more slowly than 
agglutinins. As a rule precipitins are inactuated 
at lower temperatures than agglutinins. 

When serum is heated to from 50° to 60° C. its 
ability to cause a precipitate in the homologous 
precipitogen is destroj^ed, although it may be dem- 
onstrated that the power to combine with the lat- 



Natui-e of 
Precipitins. 



Specific 
Inhibition. 



Antipreeip- 



23S INFECTION AND IMMUNITY. 

ter is unchanged. Hence precipitin, like agglu- 
tinin, is composed of two groups, a binding or 
haptophorous, and a ferment-like group in which 
the active property reside; the latter is the coag- 
ulin of the molecule. When precipitin has lost its 
coagulin it becomes precipitoid, and as precipitoid 
it may unite with precipitogen and thereby inhibit 
the action of a fresh precipitin which may be 
added later. When a precipitating serum has 
partly degenerated into precipitoids, that is, when 
it consists of a mixture of precipitin and precipi- 
toid, it is found that the latter have the greater 
affinity for precipitogen; hence, in concentrated 
solutions of the serum, precipitoid may be present 
in sufficient quantity to bind all the available pre- 
cipitogen, and the reaction would not occur in 
spite of the presence of active precipitin. This is 
spoken of as specific inhibition. The action is 
analogous to that of toxoids and agglutinoids, and 
the phenomenon is mentioned again in this in- 
stance in order to emphasize the fact that certain 
principles of action are common to many of the 
immune substances. Precipitoids, like toxoids and 
agglutinoids. are formed by long standing, by the 
action of heat and light and by other injurious in- 
fluences. 

The molecule of precipitin, like that of agglu- 
tinin, is a receptor of the second order (Fig. 6). 

The attempt has. been made to produce antipre- 
cipitins by immunization with precipitating 
serums ; this is immunization with an immune 
serum. It is reported that antibodies have been 
obtained for lactoserum, but not for bacterial pre- 
cipitins. There is a limit to the cycle of antibody 
formation. 



PRECIPITOGEX. 239 

Precipitogen may be defined as any albuminous xature of 
substance immunization with which will cause the s £"? ipit °~ 
formation of a specific precipitating serum. In 
addition to those mentioned above, albuminous 
urine, pleural exudates, ascitic fluid and that from 
hydrocele are precipitogens. The same is true of 
some albuminous fractions of serums, as globulin, 
the precipitating serum for which may be called 
antiglobulin. Kraus believes that the precipitogen 
of bacterial filtrates is associated with albuminous 
molecules. Jacoby obtained by tryptic digestion 
of ricin, a precipitogen which gives no albumin 
reaction. On the other hand, certain precipito- 
gens are destroyed by pepsin and trypsin, a fact 
which indicates their albuminous nature. 

Certain precipitogens are said to consist of a 
thermolabile and a thermostabile portion, the dif- 
ferentiation of which we need hardly consider. 

It is of no little interest that precipitogen, simi- Precipitoid 
lar to precipitin, consists of two groups, through precipitogen. 
one of which it unites with precipitin, whereas the 
other has a coagulating function. Egg albumin, 
for example, when heated to rather high tempera- 
tures, loses its ability to participate in the pre- 
cipitation reaction, although it retains its binding 
power for precipitin. In view of the fact that the 
two substances which enter into the reaction have 
similar structures, it is difficult to say which as- 
sumes the passive and which the active role. De- 
generated precipitogen is also called precipitoid. 
Id order to distinguish the two precipitoids one 
must speak of the precipitoid of precipitogen, and 
the precipitoid of precipitin. The precipitoid of 
precipitogen yields precipitin by immunization ; 
hence, it is all the more analogous to the toxoids. 






240 INFECTION AND IMMUNITY. 

precipitate. The precipitate which is caused when a bacterial 
nitrate is mixed with its specific antiserum forms 
in from one-half hour to several hours, and appears 
as a coherent white sediment which in the course 
of twenty-four hours has left the overlying fluid 
quite clear. The action of the precipitins for 
scrums is more rapid, and in either case sedimen- 
tation is hastened by placing the fluids at body 
temperature. As intimated above, the occurrence 
of the reaction depends on an intact condition of 
the coagulin groups of both substances. A low 
concentration of organic acid favors, whereas min- 
eral acids and alkalies inhibit or prevent precipi- 
tation ; a neutral reaction is indifferent. The pre- 
cipitate contains albumin, which, however, has be- 
come so changed that it is not susceptible to the 
action of trypsin. The two in combining have in 
some way shut off the point of attack for trypsin. 
A lactoserum precipitates the casein of the corre- 
sponding milk. The presence of salts is necessary 
for the reaction of precipitation. Both agglutinin 
and agglutinogen are present in the precipitate, 
but there seems to be no law governing the 
amounts of each in the combination. 

The supernatant fluid contains a remaining 
soluble part of both substances as can be shown by 
adding fresh precipitin and vice versa. 
Group Pre- Group precipitation is not so pronounced as 
^"spec^fio^ty! group agglutination, yet it exists to a certain de- 
gree and is of the utmost practical importance in 
attempting to differentiate serums by the precipi- 
tation method. Although bacterial precipitins are 
highly specific, it is important to observe the prin- 
ciple of serum dilution which was emphasized 
under agglutination, in order to obtain the adven- 



PRECIPITINS. 241 

titious precipitins in such small amounts that 
they do not interfere with the chief precipitin. 

That feature of the precipitation reaction which Forensic 
has the most practical bearing has to do with its Precipitins. 
medicolegal use in the detection of human blood. 
For this purpose it has supplanted the specific 
hemolytic serums, which are to be referred to later. 
In the course of investigations it was found that 
even the smallest dried blood stain, although 
months old, would cause the formation of a sedi- 
ment when mixed with its homologous precipitat- 
ing serum. It remained for certain important de- 
tails to be worked out in order to render the test 
sufficiently reliable for forensic work. The spe- 
cificity of the reaction appeared to be threatened 
somewhat when it was learned that the serum of 
monkeys undergoes precipitation when treated by 
an immune serum which is specific for human 
serum. This is, again, group precipitation. Ad- 
ventitious precipitation is, in fact, so widespread 
that some have felt justified in speaking of a mam- 
malian serum reaction. Hence, in order to insure 
specificity, it has become necessary to use precise 
quantitative methods in differentiating bloods or 
serums by this method. The immune serum which 
is used in the test must be diluted to some extent 
in order to eliminate accidental precipitins; but 
even a more important precaution is the volumet- 
ric measurement of the precipitate which is 
formed. The technic of Schur may be cited. Test 
tubes are so made that the lowermost portion con- 
sists of a graduated capillary tube. One c.c. of the 
fluid to be tested is placed in one of these tubes, to 
which is then added 0.2 c.c. of the precipitating 
serum. The mixture is kept at body temperature 



242 



INFECTION AND IMMUNITY. 



Identification 
of Meats. 



Colloids and 
the Reactions 

of Immunity. 



until the reaction is complete, and the sediment is 
then thrown into the capillary portion of the tube 
by centrifugation for a stated period of time 
(twenty minutes). The volume of the sediment 
may be read by the scale. Nuttall allows the sedi- 
mentation to occur naturally, with the tubes in an 
upright position. Other serums naturally must 
be used as controls. If the "unknown" blood is 
suspected of being human, a control tube must be 
prepared in which a similar amount of known hu- 
man serum is submitted to the same test. If the 
two tubes yield similar amounts of precipitate 
when they are treated with 0.2 c.c. of a precipi- 
tin which is specific for human serum, the identity 
of the "unknown" blood as that of man is estab- 
lished. To obtain the specific precipitin it is cus- 
tomary to immunize rabbits with human serum for 
several weeks. 

Another practical feature of the precipitation 
test has to do with the differentiation of meats. A 
precipitogenous substance which is characteristic 
for the animal may be extracted or pressed from 
the flesh, and will yield a precipitate when it is 
mixed with a precipitin of homologous nature. 
This is of particular interest in those countries in 
which the meat of the horse is put on the market 
as a substitute for that of beef. 

(For the relation of precipitins to anaphylaxis 
see chapter on anaphylaxis.) 

In view of the fact that the protoplasm of the 
body and the albuminous constituents of serum 
have a close relationship to, or really are, colloids, 
investigators have studied certain reactions which 
occur among the known colloids with the expecta- 
tion that the reactions of protoplasm and those of 



Colloids. 



COLLOID*. 243 

serums would receive some elucidation. Not much 
advancement can be made, however, until the prop- 
erties of colloids are more thoroughly understood. 
Substances which go into solution were classi- 
fied by the English physicist, Graham, as crystal- 
loids and colloids. Crystalloids include many in- 
organic salts. Usually they form clear solutions 
in water and exert osmotic pressure, supposedly 
because of the small size of their molecules. They 
diffuse with some rapidity and many are conduc- 
tors of electricity. Organic colloids comprise such 
substances as albumin, starch, dextrin, tannin, 
gelatin and many gums. By proper treatment of 
certain metals and their salts, inorganic colloids properties of 
may be prepared ; for example, ferric hydroxid and 
the sulphids of antimony and arsenic. When col- 
loids are dissolved in water the solutions are often 
more or less opaque, and are sometimes opalescent 
because the particles or molecules are of such size 
that they polarize light. They exist in water either 
as a solution of molecules of great size or as a sus- 
pension of considerable particles or aggregates of 
molecules. In some instances the particles are so 
large that they may be seen by a magnification of 
1.000 diameters, while in others no degree of mag- 
nification renders them visible with the ordinary 
microscope. By the use of the recently devised 
ultramicroscope, however, the finest particles in 
some colloidal solutions may be discerned. Col- 
loidal substances, such as albumin, diffuse very 
slowly and exert little or no osmotic pressure, sup- 
posedly because of the large size of the particles. 
They do not conduct electricity, but the particles 
themselves react to the electric current by altera- 
tions in the direction of their motion (i. e., toward 



244 INFECTION AND IMMUNITY. 

the positive or the negative pole), and, moreover, 
carry electric charges themselves. 
Precipitation The features of colloids which bring them into 
° Eieetroiyte«J relation with the subject in hand are their coagu- 
lable nature in certain instances and the fact that 
their particles may be agglutinated or precipi- 
tated by the addition of minute amounts of salts 
(electrolytes). In this connection one naturally 
recurs to the observation of Bordet, which was 
mentioned in the preceding chapter, concerning 
the inagglutinability of micro-organisms so long 
as salt is withheld from the solution. This anal- 
ogy would suggest that the bacteria after their 
union with agglutinin may conduct themselves as 
colloidal particles. In the precipitation of colloids 
by salts it has been suggested that the salts so 
alter the electric condition of the colloidal parti- 
cles that their surface tension is decreased, and as 
a result of this change neighboring particles 
coalesce in such quantities as to produce a visible 
sediment. 

j^eisser and Friedberger have studied certain 
colloids, having in mind the similarity of their be- 
havior to serum reactions. They found, for exam- 
ple, that two of our common dyes which are col- 
loids and bear opposite charges of electricity (eosin 
and Bismarck brown), give rise to a precipitate 
when the two are mixed. Furthermore, the spe- 
cific inhibition which may be obtained in the reac- 
tion with serum precipitins (see above) could also 
be realized with the eosin and Bismarck brown. 

The agglutination of bacteria and of red blood 
cells may also be accomplished with colloids. 
Landsteiner agglutinated erythrocytes with col- 
loidal silicic acid. 



CHAPTER XVI. 



A. GENERAL PROPERTIES OF BACTERICIDAL 
SERUMS. 

Antibacterial, bactericidal and bacteriolytic are Bacteriolysis 
three terms which are used in a rather loose, inter- ?™ S i n . ac 
changeable way, although they are not strictly 
synonymous. A bactericidal serum is one which is 
able to kill bacteria, as the term implies ; if at the 
same time it dissolves the organisms it is bacterio- 
lytic. Inasmuch as some serums, as antityphoid, 
do kill bacteria without dissolving them, while 
others, as anticholera, have- the dissolving power, 
the distinction has a certain significance. In either 
case the serum is, of course, antibacterial. For 
lack of a more concise English term, bacteriolysis 
is used to designate the process in which bacteria, 
with or without solution, are killed by serums. 
Bacteriolysin refers to the substances in serum 
which accomplish this action. The means of de- 
termining the bactericidal power of a serum are 
indicated on page 254. True bacteriolysis is best 
observed with the organism of cholera and its 
antiserum as described later under the title of the 
Pfeiffer experiment. 

Bacteriolysins are far more complex than anti- 
toxins, agglutinins and precipitins. One may best 
appreciate their nature as understood at present 
by tracing their development from the relatively 
simple alexins of Buchner. 

Following the investigations of Fodor, Behring Alexins. 
and others, which showed that normal blood may 



246 INFECTION AXD IMMUNITY. 

kill bacteria in the test-tube, and after additional 
facts were obtained by Nuttall, Buchner demon- 
strated that it is not necessary to use the full blood 
in order to obtain the bactericidal action, but that 
serum alone has a similar effect. He spoke of the 
antibacterial substances collectively as alexins 
(substances which ward off), taking the reason- 
able view that natural immunity to bacteria de- 
pends on their presence in the body. The increased 
bactericidal power of the serum which develops 
during immunization or infection with certain 
micro-organisms goes hand in hand with the in- 
creased resistance of the individual against the 
infection. The alexins have undergone a specific 
increase; they are now immune alexins or, as we 
say to-day, immune bacteriolysins, and it is sup- 
posed that acquired immunity, in these instances, 
depends on their new formation. 
selective Alexins were very sensitive substances; they dis- 
appeared spontaneously from serums in a few 
days, were destroyed by a rather low degree of 
heat (55° C), by acids and alkalies, and were 
active only in the presence of certain salts, espe- 
cially sodium chloric!. A striking feature of 
alexins, as distinguished from chemical bacteri- 
cides, was their marked selective action on bac- 
teria. The alexins of animal A might destroy one 
micro-organism readily and affect another little or 
none at all, whereas those of animal B might have 
different selective characteristics. 
The Phenom- Work which was instituted by Pfeiffer and de- 

enon of , 

pfeiffer. veloped further by others led the way to a more 
correct understanding of the nature of alexins. 
Pfeiffer studied the bactericidal action of serums 



PFEIFFER'S PHENOMENON. 247 

in the body of the living animal, i. e., in the peri- 
toneal cavity. His most classic results were ob- 
tained with the organism of cholera. A guinea- 
pig is immunized against this micro-organism by 
injections of the killed or living bacteria. We have 
already learned of this process as that of active 
antibacterial immunization. When the animal is 
well immunized the experiment is begun by the 
intraperitoneal injection of a quantity of culture 
which would be fatal to an unimmunized animal. 
At intervals during the next twenty or thirty min- 
utes small amounts of peritoneal fluid are removed 
for .microscopic examination by means of fine 
pipettes which have been drawn out in the flame. 
The abdominal wall is punctured with the pi- 
pette through an incision in the skin and the 
fluid flows into the tube by capillary attraction. 
A portion of the fluid is examined as a hanging- 
drop or dried on a cover-glass, fixed in the flame 
and stained with a dilute solution of carbol- 
fuchsin. In the hanging-drop it is first noticed 
that the organisms have lost their motility; the 
comma-shaped and S-shaped forms soon become 
spherical and at first appear swollen and clear, 
whereas in later preparations they gradually de- 
crease in size and show a very rapid vibrating 
movement, the so-called Brownian movement 
which is purely physical in nature. In the course 
of from twenty to thirty minutes the organisms 
have been completely dissolved. These changes 
may be followed in the stained specimens, in which 
the altered cells eventually appear as fine reel 
granules. 

As Metchnikoff, Bordet and others have shown, The Esperi- 

., .. . -,.-i.,i in -j ment in Vitro. 

the same result may be obtained without the inter- 



by the Ti.«* 

sues. 



248 INFECTION AXD IMMUNITY. 

vention of the animal body, by mixing perfectly 
fresli anticholera serum with the vibrios and 
mounting as a hanging-drop preparation. The 
slide must be kept at the temperature of the body 
by means of a warm stage. The reaction, how- 
ever, is far less vigorous than when it takes place 
in the peritoneal cavity and the solution of the 
cells may not be complete. No bacterium is so 
completely dissolved under these conditions as the 
vibrio of cholera, although the typhoid bacillus and 
similar organisms undergo some changes in their 
form. 
The Activa- The experiment of Pfeiffer may also be con- 
active sernin ducted in the abdominal cavity of a non-immune 
guinea-pig by injecting anticholera serum in con- 
junction with the culture (passive antibacterial 
immunization) . This is the classic Pfeiffer experi- 
ment. The immune serum should be of such 
strength and should be given in such quantity that 
the animal is saved in spite of the ten fatal doses 
of culture which the typical experiment demands. 
Experiments brought to light a condition which 
seemed paradoxic; an old immune serum which 
had lost its bactericidal power as manifested in 
vitro, or one in which the alexins had been de- 
stroyed by a temperature of 60° C, showed its 
original protective power in the animal experi- 
ment. Furthermore, when an inactive immune 
serum was injected into the abdominal cavity, al- 
lowed to remain for a time and then withdrawn, 
its bactericidal power for experiments in vitro was 
found to be re-established. On the basis of these 
facts, Pfeiffer concluded that the specific sub- 
stance is present in the immune serum in an inac- 
tive form, and that it becomes active as a resnlt 



PFEIFFER'S PHENOMENON. 249 

of contact with living tissue cells, supposedly the 
endothelial cells of the peritoneum. According to 
this conclusion, an inactive serum could become 
active again only after its introduction into the 
body. 

It remained for Bordet to show, on the con- in activation 
trary, that contact of the serum with living cells tion. 
is not necessary to render it active for bacterici- 
dal experiments in vitro. It is sufficient to add 
to the heated immune serum a small amount of 
fresh normal serum from some normal animal, 
the quantity of normal serum which is used not 
being in itself bactericidal. Under these condi- 
tions, then, we have to do with two serums which, 
when combined, are bactericidal, but when sepa- 
rated are inactive. The destruction of the active 
property of a serum by heat or by other means is 
called inactivation, and the re-establishment of its 
power by the addition of fresh normal serum is 
reactivation. The immune serum, when heated to 
55 to 60° C, loses something which is essential to 
its activity, and this something may be replaced 
by the normal serum. That the substance in the 
normal serum is identical with that which was de- 
stroyed in the immune serum is indicated by the 
fact that it is destroyed by the same degree of 
heat; a heated normal serum will not reactivate 
an immune serum. 

The conclusion of Bordet that the bactericidal two sub- 

<> -. -. ., , . -, .. stances in a 

power oi a serum depends on the combined action Bactericidal 
of two substances has been substantiated by numer- Serum - 
ous investigators. These are the substances which 
in recent years have become familiar under the 
names of amboceptor and complement and their 
various synonyms (see p. 256). One of them, the 



250 1XFECTION AND IMMUNITY. 

amboceptor, is heat-resistant (thermostable), i. e., 
it is not destroyed at 56° C, whereas the other, 
the complement, is susceptible to heat (therm o- 
labile), being destroyed at that temperature which 
killed the alexins of Buchner. The term alexin 
is still applied by some writers to the thermolabile 
substance (complement), its original significance 
having been modified. 
iificity. The specificity which prevails among antitoxins 
and agglutinins is found also in the action of bac- 
tericidal serums. When an anticholera serum is 
injected into the peritoneal cavity of a guinea- 
pig, protection is not afforded against other vibrios 
or other pathogenic organisms. The specificity is 
so great that the reaction of Pfeiffer may be used 
for the identification of bacteria. If one has in 
hand an unknown vibrio, its identity or non-iden- 
tity as the organism of cholera may be determined 
by injecting it, in conjunction with anticholera 
serum, into the peritoneal cavity of a normal 
guinea-pig; if the microbe is transformed into 
granules it is the vibrio of cholera, otherwise it is 
not. Other bacteria may be identified in a similar 
manner by the use of the proper serums. In spite 
of this high specificity, the group reaction may 
Reac- occur even with bactericidal serums. An anti- 
typhoid serum, for example, shows its strongest 
bactericidal power for the t3 r phoid bacillus, al- 
though it is at the same time more destructive for 
closely related organisms, as the colon bacillus, 
than a normal serum from the same species. By 
diluting the serum sufficiently the adventitious 
bacteriolysins are so nearly eliminated that the 
specificity of the serum for its homologous organ- 
' ism becomes manifest. 



tion. 



BACTERICIDAL SERUMS. 251 

Bactericidal serums are not obtained with equal 
readiness for all micro-organisms. We are most 
familiar with those which are yielded by immuni- 
zation or infection with the microbes of cholera, 
typhoid, plague, the colon bacillus and related bac- 
teria. Many other bacteria, as the pneumococcus, 
streptococcus, tubercle bacillus and others, yield 
neither antitoxins nor bactericidal substances. In- 
asmuch as recovery from such infections is an ex- 
pression of acquired immunity, no matter how 
temporary it may be, it is evident that not all ex- 
amples of acquired immunity can be explained on 
the basis of the serum properties which we now 
recognize. This will be referred to again in rela- 
tion to phagocytosis (Chapter XVIII). 

Experiments of some importance have to do 
with the ability of bacteria to absorb the homolo- 
gous bactericidal substance from a serum when the 
two are mixed in test-tubes. Hence, if natural 
antibacterial immunity depends on the bacterioly- 
sin which is present in the circulation, a large 
mass of the bacterium when injected intravenously 
should absorb or fix the bactericidal substances ; as 
a consequence, serum which is drawn later should 
show a great decrease in its bactericidal power for 
the organism which was injected. Although re- 
sults of this nature have been obtained by a num- 
ber of competent investigators, they are not with- 
out exception. In the same connection fatal infec- 
tions should be accompanied by a decrease of the 
natural bactericidal power of the serum for the 
organism involved. This has been found to be true 
in man in relation to plague, and in some animal 
infections. 



Endotoxins 



•252 INFECTION AND IMMUNITY. 

The Effect of In a preceding chapter micro-organisms were 
serums 'on divided, first, into those which secrete soluble tox- 
N ins, immunization with which causes the forma- 
tion of antitoxins, and, second, those which do not 
secrete such toxins and for which no manipula- 
tions known at the present time are successful in 
stimulating to the formation of antitoxins. These 
lines, however, can not be drawn sharply, for there 
are a few micro-organisms which, according to 
manipulation, cause the formation of either an 
antitoxic serum or a bactericidal serum. In gen- 
eral it may be said that the character of the serum 
depends on the bacterial constituent which is used 
for immunization. If the diphtheria bacillus it- 
self, or the pyocyaneus bacillus, is injected, the 
toxin having been washed away, bactericidal ser- 
ums are formed, whereas if toxins alone are intro- 
duced, antitoxins are the result. After all, it 
seems plain that the bacteria of the second group 
must be pathogenic, because of toxic substances 
which they carry with them into the body. In 
view of the fact, however, that they do not secrete 
soluble toxins in culture media, it is held that 
their toxic properties are integrally associated with 
the bacterial protoplasm; they are the endotoxins 
spoken of previously. 

The question naturally arises: Does a bacteri- 
cidal serum in dissolving or killing its homologous 
organism neutralize the endotoxin at the same 
time? On the basis of very positive experiments 
which have been performed, especially by Pfeiffer, 
it is evident that the serum has no such action. In 
the experiment of Pfeiffer, one may inject into the 
abdomen a sufficient quantity of anticholera serum 



BACTERICIDAL SERUMS. 253 

to kill all the organisms which have been intro- 
duced, and yet the animal may die with the intoxi- 
tion of cholera. Furthermore, if one considers a 
culture of the cholera vibrio, which has been killed 
by heat, as representing so much cholera toxin, 
anticholera serum protects against no more of it 
than does the same quantity of normal serum. It 
is believed that anticholera and similar ■ immune 
serums may even increase intoxication by dissolv- 
ing the bacteria and thus liberating an excess of 
endotoxin. 

We have little positive knowledge concerning the origin of 
organs which form the bactericidal substances in substances. 
acquired immunity. Pfeiffer and Marx, in rela- 
tion to cholera, and Wassermann in typhoid, found 
that the spleen and the hemopoietic organs in gen- 
eral contain the immune bodies in greater concen- 
tration than the blood serum, and in immunization 
experiments the bodies may be demonstrated in 
these organs at a time when they are absent from 
the circulation. This fact is generally accepted as 
proof of their formation at these points. Wasser- 
mann and others have demonstrated the presence 
of complement in the leucocytes, and Metchnikoff 
holds that it is produced only by such cells. (See 
origin of agglutinins, Chapter XIII.) 

The standardization of bactericidal serums is at f *£tion Pd ~ 
present more of theoretical than of practical in- 
terest, because of their limited therapeutic use. 
Their values can not be determined with the ac- 
curacy with which one measures a unit of anti- 
toxin. One may deliver from a pipette a definite 
quantity of toxin and if the toxin has been well 
preserved the same quantity may be obtained at 



254 INFECTIOH AND IMMUNITY. 

any subsequent time. On the other hand, it is impos- 
sible to preserve a culture of living bacteria so that 
the number of the organisms and the virulence 
of the culture remain constant, nor will two cul- 
tures made at different times contain the same 
number of cells in a given volume. "Hence, stand- 
ard cultures which are necessary for the systematic 
valuation of serums are not easily available. One 
may use a definite volume of a bouillon culture of 
an organism which has grown for a certain number 
of hours, but in all likelihood no two cultures 
would contain the same number of organisms. 
Pfeiffer uses the normal loop which has been men- 
tioned, i. e., one which will take up from a surface 
of agar two milligrams of the bacterial mass. The 
culture must have grown for a definite period, 
eighteen to twenty-four hours. Tests having some 
value may be made in the test-tube with the fresh 
or complemented serum. This, however, gives one 
only the bactericidal power as it is manifested out- 
side the body, and it may not be a correct index of 
the protective power of the serum when it is in- 
jected into the living animal. For the test-tube 
experiment various dilutions of the serum are 
made, as 1 to 10, 1 to 100 and 1 to 1,000, and a 
similar quantity of each dilution, properly comple- 
mented, is mixed with a given mass of the culture ; 
the mixtures are then placed in the thermostat for 
a number of hours. At the end of this time plate 
cultures are made from each of the mixtures, the 
plates put aside for twenty-four hours, and the 
colonies which have developed are then counted. 
The quantity of serum required to kill all the bac- 
teria may be taken as the basis for computing its 
bactericidal value. 



BACTERICIDAL SERUMS. 255 

When the protective power of the serum is de- 
termined by animal experiment it is not essential 
to use the serum when fresh; in fact, the native 
complement in the immune serum may be disre- 
garded, or, prefer ably, it may be destroyed by heat. 
If the latter procedure is adopted, or if an old 
serum is used in which the complement has de- 
generated, its reactivation is accomplished through 
the complement which is present in the body of the 
experiment animal. There are reasons for believ- 
ing that a given antiserum requires a particular 
complement for its reactivation, and that this 
complement may be present in some animals and 
absent in others; this will be referred to again. 

To find the value of anticholera serum Pfeiffer 
prepares dilutions similar to those mentioned 
above, and to the same quantity of each dilution 
adds ten fatal doses of a virulent culture of the 
vibrio of cholera. These are injected into the 
peritoneal cavities of guinea-pigs and after periods 
of from forty to sixty minutes hanging-drop prep- 
arations are made from the peritoneal fluid of each 
animal to determine the formation of the charac- 
teristic granules ; the highest dilution which causes 
this change in the cells stamps the value of the 
serum. The animal must at the same time be pro- 
tected against the ten fatal doses of the culture. 

The value of an antityphoid serum may be de- 
termined in the same way, the result being judged 
by the protection which is afforded the animal 
rather than by the formation of granules. 

Antityphoid, antiplague, and some other serums 
are also tested by injecting the serum twenty-four 
hours in advance of the culture. 



256 IXFECTIOX AXD IMMUNITY. 

It is necessary to know the virulence of a cul- 
ture with which an antiserum is tested. It is pos- 
sible to maintain some organisms at a rather con- 
stant virulence by passage, i. e., infecting animals 
with the microbe and recultivating it from the 
tissues. With others, abundant controls must be 
made at the time the serum is tested in order to 
know at that moment the precise virulence of the 
culture. In all probability it requires more serum 
to protect against very virulent cultures than 
against those of less virulence. 

B. HEMOLYSINS. 

Experimental The simplicity of hemolytic experiments and the 
Hemolysins, rapidity with which they may be performed and 
terminated have rendered hemolytic serums par- 
ticularly useful in the study of amboceptors and of 
complements, for we are to understand that such 
serums are toxic to erythrocytes only because of 
the amboceptors and complements which they con- 
tain. The most important facts which have been 
learned concerning the action of hemolytic serums 
have been found to hold true for bactericidal 
serums as well; hence it is an indifferent matter 
if principles which are common to both are illus- 
trated by frequent references to serum-hemolysins. 
Teciinic of The corpuscles for hemolvtic experiments arc 

Hemolytic r •> *«■,-*-, 

Experiment, obtained by the defibrination of freshly-drawn 
blood and the removal of the fibrin. Usually they 
are made into a 5 per cent, suspension by dilution 
with isotonic (physiologic) salt solution. Inas- 
much as the serum which is present may interfere 
with the action of the complement or amboceptors 
of the hemolysin, it is customary to remove it by a 
washing process. The 5 per cent, emulsion, or the 



HEMOLYSINS. 257 

undiluted blood is ccntrifugatecl, the overlying 
fluid drawn off by means of a pipette and substi- 
tuted by fresh salt solution; the corpuscles are 
thoroughly mixed with the new solution and the 
process of centrifugation repeated, the corpuscles 
finally being diluted to the original volume with 
salt solution. After from two to four washings 
any residual serum usually may be disregarded. 
To test the hemolytic power of a serum one meas- 
ures identical quantities of the 5 per cent, washed 
blood into each of a series of test-tubes by means 
of a graduated pipette and then adds increasing 
quantities of the serum to succeeding tubes. All 
tubes are then diluted to equal volumes by means 
of salt solution, as it is of some importance to 
maintain a uniform concentration of the cor- 
puscles. The contents of the tubes are mixed 
evenly by shaking and the series is placed in the 
thermostat for about two hours; this temperature 
is necessary for complete and rapid action of the 
toxic substances. At the end of this time the tubes . 
are placed in the ice chest and left over night in 
order that the cells may settle to the bottom, Or 
sedimentation may be accomplished at once by 
centrifugation. 

In either case, the overlying fluid is colored red Hemolysis 
by the dissolved hemoglobin in proportion to the 
extent of destruction of the erythrocytes. In case 
solution has been complete, the sediment is indis- 
tinct and colorless, being made up only of the 
stromata of cells, whereas in the tubes showing 
only partial hemolysis the sediment is red and has 
an indirect quantitative ratio to the coloration of 
the overlying fluid. By suitable variations in the 
amounts of serum used in different tubes, its 






258 INFECTION AXD IMMUNITY. 

exact dissolving dose for the given volume of cor- 
puscles may be determined. Although the term 
hemolysis is a perfectly proper one, we are to un- 
derstand that serums cause solution of the hemo- 
globin, but not solution of the whole cell ; we speak 
loosely of solution of the corpuscles. 
similarity After Bordet had shown the analogy between 
Bactericidal bactericidal and hemolytic serums, and after the 
lytic Action", phenomena of inactivation and reactivation had 
been developed by Bordet and Metchnikoff, Ehrlich 
and Morgenroth undertook the study of ambocep- 
tors and complements as they occur in hemolytic 
serums. The facts ascertained by them and the 
methods of research which they devised have pro- 
vided many investigators with a starting point for 
work of the highest importance concerning the 
bactericidal serums and antibacterial immunity, 
and their interpretations, moreover, served to ex- 
tend the side-chain theory of immunity to its pres- 
ent comprehensive limits. 

For the sake of convenience one may speak of a 
heated immune serum, or one in which the com- 
plement has become inactive from age, as a solu- 
tion of amboceptors, disregarding temporarily the 
agglutinins, precipitins and perhaps other bodies 
which the serum contains. Also, since fresh nor- 
mal serums are rich in complements and usually 
contain but a small amount of any one amboceptor, 
they may conveniently be considered as solutions 
of complements; yet normal serums may not be 
considered as pure complement and used as such 
in unlimited quantities for actual experiments, be- 
cause of the bacteriolysins and hemolysins which 
many contain. Only a quantity of the normal 
serum which in itself is not toxic for the cell 



HEMOLYSINS. 



259 



may be used for complementing purposes, and this 
may be as low as, or lower than, 0.1 c.c. for a par- 
ticular experiment. 

As pointed out in the preceding chapter, the T . he Absorp- 
combined action of amboceptor and complement is boceptors by 
necessary for the cytotoxic action of a serum. In 
view of the fact that the toxic power is lost by ex- 
posure to that temperature which destroys comple- 
ment, it seems that the latter is the actual dis- 
solving or toxic substance, whereas the ambocep- 
tor must play some intermediary role. Investiga- 
tions have shown that the two act together in a 
very definite manner in that the absorption of the 
amboceptors by the cells is a prerequisite for the 
absorption and action of the complement. This 
may be verified by simple experiments: Mix 
erythrocytes with the homologous amboceptors, 
and after a period of from twenty to thirty min- 
utes centrifugate the mixture and remove all the 
free serum from the cells by repeated washings 
with isotonic salt solution. If the cells are again 
suspended in salt solution and a small amount of 
complement is added and thoroughly mixed, the 
hemoglobin is dissolved out; a control must, of 
course, show that the complement alone has not 
the dissolving power. The result indicates that 
the erythrocytes during their contact with the im- 
mune serum had absorbed or combined chemically 
with the amboceptors, and that the latter remained 
attached to the cells in spite of the washings to 
which they were submitted. 

It would seem that the union of amboceptor 
with cell has the effect of rendering the latter sus- 
ceptible to the action of complement, and for this 
reason amboceptor-laden cells are spoken of as 



Sensitiza- 
tion. 



INFECTION AND IMMUNITY. 



Order of Ac- 
tion of Ambo- 
ceptor and 

Complement. 



Cytophilous* 
Haptopliore 
of the Ambo- 
ceptor. 



sensitized cells. Hence, according to the cells and 
serums employed, we may refer to sensitized 
erythrocytes, sensitized bacteria, etc. The experi- 
ment is called the sensitizing, absorption or bind- 
ing experiment. An immune serum may be de- 
prived of all its amboceptors in the binding ex- 
periment if a sufficient quantity of cells has been 
used, and it would thereby be rendered incapable 
of further reactivation by the subsequent addition 
of complement. 

If, instead of performing the experiment in the 
manner described, the process is reversed so that 
the corpuscles are first treated with the solution 
of complement and then with the amboceptors, the 
corpuscles are not hemolyzed. During the wash- 
ing process the complement is entirely separated 
from the cells, and from this fact it is clear that 
direct union between corpuscle and complement 
does not occur; only sensitized cells take up com- 
plement. 

The question as to whether the corpuscles in 
taking up amboceptors do so by chemical combina- 
tion or by physical absorption has been contended 
with some vigor. Ehrlich believes that the process 
is one of chemical union, and if one adheres to this 
view it becomes necessary to assign binding or 
haptophorous groups both to the red blood cells 
and to the amboceptors. In contrast to another 
haptophore which the amboceptor possesses and 
which will be described below, that one which 
unites with the cell is called the cytophilous hapto- 
phore. The haptophore of the ervthrocyte which 
enters into the union is an essential part of a re- 
ceptor of the red cell, consequently we say that the 
amboceptor unites with a receptor of the corpuscle. 



HEMOLYSINS. 261 

The heating of serum to 56° C. provides one }! lie ai»so*p- 

° - 1 tion Experi- 

means of apparent isolation of the amboceptor ment in the 
from the complement, but this is not a true isola- 
tion in that complement is merely rendered inac- 
tive by the heat rather than totally eliminated. 

Ehrlich and Morgenroth devised a method by 
which the amboceptors may be separated from a 
fresh immune serum without in any way injuring 
the complement. This is accomplished by per- 
forming the binding experiment, already alluded 
to, at a low temperature. The serum, containing 
both amboceptors and complement, is cooled to 0° 
C. or slightly above, by means of a freezing mix- 
ture of salt and ice. A suspension of the homolo- 
gous corpuscles is cooled to the same point, the 
serum is added and the mixture maintained at 0° 
to 4° C. for from fifteen to twenty minutes. At the 
end of this time the sensitized cells are removed 
by immediate centrifugation at a low temperature, 
and are washed entirely free from serum by the 
use of ice-cold salt solution. If the low tempera- 
ture has been adhered to rigorously and the work 
done quickly, the corpuscles are not laked during 
the manipulations in spite of the presence of both 
amboceptors and complement. Furthermore, the 
washed sensitized cells remain intact even when 
their temperature reaches that of the thermostat, 
whereas if some fresh normal serum or the serum 
from which the amboceptors were absorbed is 
added, they undergo hemolysis as readily as when 
treated with the active immune serum. The 
original immune serum is now a solution of com- 
plement, and fresh corpuscles which are added to 
it are not dissolved because of the absence of ambo- 
ceptors. 



2C2 



INFECTION AXD IMMUNITY. 



Coiuplement- 
ophilous 
Haptophore 
o£ Ambocep- 
tor. 



Action of 
Amboceptors. 



These results show the following important 
facts: Amboceptor and complement exist side by 
side in an immune serum, not as a united sub- 
stance. Union of amboceptor with cell is inde- 
pendent of complement, the latter being taken up 
only after the amboceptor-cell reaction has oc- 
curred. Amboceptors unite with cells at a low 
temperature, whereas complement requires a 
higher temperature for its union and for the fer- 
ment-like activity by which it dissolves or kills the 
cells. 

That constituent of the amboceptor which 
unites with 'the cell has been referred to as the 
cytophilous haptophore. Ehrlich and his follow- 
ers believe that complement in establishing con- 
nection with the cells does so by combining with a 
second haptophore of the amboceptor, after the 
latter has sensitized the erythrocyte or bacterium. 
Hence, an amboceptor has, as the name implies, 
two receiving groups or haptophores, the second 
being the complement ophilous haptophore (Fig. 
7). It is hardly desirable to discuss various ex- 
periments which furnish additional evidence of the 
amboceptor nature of the thermostabile body. The 
observed phenomena allow one to assign to it the 
two haptophores mentioned. 

There is a conflict of ideas as to the nature of 
the change produced by the amboceptors, as a re- 
sult of which the cells are made susceptible to the 
action of complement. Bordet speaks of the am- 
boceptor as the substance sensibilisatrice, the sen- 
sitizing substance; and his conception of the ac- 
tion of the two substances he has compared rough- 
ly to the opening of a lock for which two keys are 
demanded. One key, amboceptor, is needed to 



MECHANISM OF HEMOLYSIS. 263 

prepare the lock for the action of the second key, 
complement, the latter being the one which really 
opens it. 

Metchnikoff applies the name fixator to the 
thermostabile body, having in mind the action of 
a mordant in preparing tissues or other substances 
for the reception of a dye; this differs little from 
preparatory the word used by Gruber. 

The idea of Ehrlich, however, is distinctly at 
variance with the conceptions mentioned, for he 
sees in the union of amboceptor with cell nothing 
more than the introduction of a new chemical 
affinity, i. e., one which attracts complement, and 
this new affinity does not lie in the cell itself, but 
rather in the amboceptor (complementophilous 
haptophore) after the union has occurred. Hence, 
the terms intermediary body (Zwischentcorper) , 
copula of Miiller, and desmon of London, are 
words which carry with them the meaning that the 
amboceptor first unites with the cell and then acts 
as a linking substance through which complement 
finally is put in relation to the cell. This also is 
the meaning embodied in the amboceptor of 
Ehrlich, the word indicating more accurately his 
conception of the method by which the substance 
acts as an intermediary body. 

If we consider it established that in the process structure of 

» . , , . i , t Complement. 

of cytolysis union occurs between complement and 
amboceptor we must at the same time assign a 
haptophorous group to complement. Union would 
be impossible without it. Corroborative proof of 
the existence of this haptophore lies in the fact 
that immunization with complement results in the 
formation of anticomplement, a prerequisite for 
which is union of complement with cell receptors 



mentoid. 



264 INFECTION AND IMMUNITY. 

in the immunized animal ; and this union, it seems 
necessary to assume, takes place through a binding 
group. The mere possession of a haptophore, how- 
ever, does not account for the ferment-like activity 
of complement. The latter characteristic resides 
in the so-called zymotoxic group ; hence, comple- 
ment, having a binding and a toxic group, has a 
structure like that of a toxin. 
Compie- Somewhat loosely we have said that the inactiv- 
ity of a serum which has been heated to 56° C. 
depends on destruction of the complement. This 
is not strictly true, however, for such treatment 
destroys only the zymotoxic group, the haptophor- 
ous constituent remaining uninjured. Comple- 
ment altered in this respect is called complemen- 
toid, and it is analogous to toxoid, agglutinoid and 
precipitoid. Two essential facts go to show that 
this is the principle change wrought by heating. 
First, the fact stated above, that immunization 
with complementoid, causes the formation of 
anticomplement. Second, complementoid may 
exceed true complement in its affinity for the 
amboceptor, and if sensitized cells are treated with 
a serum containing a mixture of complement and 
complementoid, the latter may occupy completely 
the complementophilous haptophores of the ambo- 
ceptors and thus may block the way for action on 
the part of complement. This is again the spe- 
cific inhibition which has been mentioned in con- 
nection with toxoids, agglutinoids and precipi- 
toids. This is the Complementoid-Verstopfung 
(complementoid obstruction) of Ehrlich. 
Formation The amboceptor, as the characteristic property 
of a bactericidal or of a hemolytic serum, is a spe- 
cific product of the immunization, whereas the 



of Ambocep- 
tors. 



FOE MAT I OX OF AMBOCEPTORS. 2G5 

amount and character of complement in the im- 
munized animal undergoes little or no change. 
We are, of course, obliged to consider the ambo- 
ceptors as a product of the cells of the body. In 
the terminology of Ehrlich, they are discarded cell 
receptors, and with their two haptophores repre- 
sent a more complex structure than either the re- 




Fig. 7. — Graphic representation of receptors of the third 
order, and of some substance uniting with one of them. 
c, Cell receptor the third order, an amboceptor ; e, one of the 
haptophores of the amboceptor, with which some food sub- 
stance or product of bacterial disintegration, f, may unite ; 
g, the other haptophore of the amboceptor with which com- 
plement may unite ; K, complement ; h, the haptophore, and 
z, the zymotoxic group of complement. From Ehrlich's 
"Schlussbetrachtungen," Nothnagel's System of Medicine, 
vol. viii. 

ceptors of antitoxin or agglutinin; the latter are 
uniceptors; the former amboceptors, and because 
of their higher differentiation Ehrlich has called 
them receptors of the third order (Fig. 7). 






206 



INFECTION AND IMMUNITY. 






Specificity of 
Bactericidal 

Amboceptors 
and Comple- 
ments. 



When micro-organisms gain entrance to the 
body they are killed and dissolved in considerable 
masses. As a result of the solution, certain bac- 
terial constituents reach the circulation, and 
among them are molecules or receptors which pos- 
sess haptophores capable of uniting with a par- 
ticular type of amboceptor, the latter being an in- 
tegral part of some tissue cells. This union hav- 
ing taken place, an affinity for circulating com- 
plement may be created as in the test-tube experi- 
ments. We have thus the possibility of stimula- 
tion of the cell by the bacterial constituent itself 
as a toxic or unusual food substance, or the toxic 
action may be caused by products of disintegra- 
tion of the bacterial substance, the disintegration 
having been accomplished by the digestive action 
of the complement which was taken up by the am- 
boceptor. The effect is that of an unusual stimu- 
lation, in response to which the cell, if not fatally 
injured, reproduces many amboceptors correspond- 
ing 1o the type which was occupied or injured. 
As in the formation of other antibodies, the new- 
formed amboceptors reach the general fluids of the 
body. 

Concerning the specificity of serum-hemolysins 
and serum-bacteriolysins for their homologous 
cells, we, of course, refer to the specificity of the 
whole amboceptor-complement complex. It is nec- 
essary to throw the responsibility on both sub- 
stances, because of the variations which exist 
among complements as well as among ambocep- 
tors. Inasmuch, however, as the heat-resistant 
body alone is increased during immunization or 
infection, the greater part of the specificity would 



BACTERIAL RECEPTORS. 267 

seem to depend on the nature of the amboceptor 
rather than on that of complement. 

All bacteria which stimulate to the formation Bacterial 
of bactericidal serums do so because of certain re- Receptors - 
ceptors which they possess. These are, of course, 
analogous to the receptors of erythrocytes which 
cause the production of the hemolytic bodies in 
serum. Bacteria have, in addition, many other re- 
ceptors, some of which cause the development of 
agglutinins. In the latter instance we speak of the 
agglutinogenic receptors of the cells, but there is 
no name of equal convenience which is used to 
designate the receptors which stimulate to the 
formation of amboceptors. No two micro-organ- 
isms contain an identical receptor apparatus; if 
the contrary were the case their antiserums would 
coincide in their bactericidal action. Therefore, the 
cell receptors (amboceptors) with which they unite 
during immunization differ correspondingly in 
their cytophilous haptophores. The cytophilous 
haptophore of the typhoid amboceptor finds its 
specific counterpart in the typhoid bacillus, and 
finding no such counterpart in the vibrio of chol- 
era, the latter can not be sensitized by the anti- 
typhoid serum ; on this fact depends the specificity 
of the serum. This conception does not interfere 
with the explanation of the group reaction among 
bactericidal serums, for it is conceivable that the 
colon bacillus, for example, has, in addition to 
those receptors which characterize the organism, a 
small percentage of receptors which are identical 
with those characterizing the typhoid bacillus. In 
accordance with this possibility an antityphoid 
serum may well, as it does, show some increased 
bactericidal power for closely related organisms. 



2G8 



INFECTION AND IMMUNITY. 



3Inltiplicity 
of Comple- 









Hence the explanation of group bacteriolysis is 
identical with that of group agglutination. 

There is a wide difference of opinion regarding 
the unity of complement, or alexin, its synonym. 
Bordet and his followers stand for the unity of the 
alexins, and their position rests on the fact that a 
given normal serum may be used to activate many 
different amboceptors. We should appreciate that 
this phenomenon might depend on the broad range 
of action of a single complement, or on the pres- 
ence of different complements each being specific 
for a particular amboceptor. Ehrlich and his 
school take the latter view and have actually dem- 
onstrated a multiplicity of complements in a few 
instances. Ehrlich and Sachs treated fresh nor- 
mal serums (complement) in various ways, such 
as digestion with papain, partial destruction with 
alkalies, heat. etc.. and were able by these methods 
to destroy the complement for one kind of ambo- 
ceptor, while the serum still retained its power for 
activating other amboceptors. Accordingly, it 
seems clear that the ability of a normal serum to 
activate a given amboceptor depends not only on 
the presence of complement in a general sense, but 
on the presence of a suitable complement, i. e., one 
the haptophore of which corresponds to the com- 
plementophilous haptophore of the amboceptor. 
This point is of great importance in reference to 
the treatment of infectious diseases with antibac- 
terial serums, for the efficacy of the serum would 
seem to depend on the introduction of suitable 
complement in conjunction with the amboceptors, 
or on the existence of such complement in the body 
of the patient. 



COMPLEMENT AXD ANTICOMPLEMENT. 269 

Added proof of the multiplicity of complements Antieoin " 
has been obtained by experiments with anticom- 
plements. As stated, the latter are obtained by 
immunization of suitable animals with normal or 
immune serums which contain complement or com- 
plementoid. When they are mixed with the homolo- 
gous complements the haptophores of the latter 
are bound by means of the haptophores of the anti- 
complements. The evidence of this union lies in 
the fact that a complement which has been treated 
with its specific anticomplement is no longer able 
to activate the appropriate amboceptor (p. 280). 
With properly selected serums, it may be shown 
that a given anticomplement will neutralize a com- 
plement which is specific for one amboceptor, but 
will have no effect on another complement which 
activates a different amboceptor. Hence, comple- 
ments differ at least in this respect that not all have 
identical haptophores. Immunization with leuco- 
cyte?, cells which contain complement, also causes 
the formation of anticomplement. Both natural 
and acquired antibacterial immunity may be low- 
ered by the injection of anticomplement which is 
homologous to the complement of the animal. 

Some time ago, Ehrlich expressed the opinion 
that an amboceptor in certain cases may have more 
than one cornplementophilous haptophore; in 
other words, that it may be a polyceptor rather 
than an amboceptor. This has again been empha- 
sized recently by way of explaining the ability of 
an amboceptor to absorb from a normal serum not 
only the complement which serves to activate the 
amboceptor, but also others which happen to be 
present in the serum. The former is spoken of as 
the dominant complement and the latter as non- 



270 



1 A FE( TION AND 7.17.1/ UX1TY. 



dominant complements. Figure 8 is an illustra- 
tion of such a polyceptor. 
Antiambo- If one immunizes with an immune serum the 
product is spoken of in a general way as an anti- 




Fig. 8. — Illustrating the amboceptor with more than one 
complementophilous haptophore (a polyceptor). a, Cell re- 
ceptor ; 6, cytophiHus haptophore of the amboceptor ; c, the 
dominant complement ; d, the non-dominant complements ; 
, the heptophore of the amboceptor for the dominant com- 
plement;/?, those for the non-dominant complements. (From 
Ehrlich and Marshall.) 

immune serum. The latter contains, as stated, 
anticomplement, and through the agency of this 
substance the antiserum antagonizes the action of 
the serum which was used for the immunization. 



AX TI AMBOCEPTORS. 271 

Inasmuch, however, as the immune serum contains 
amboceptors also, the antagonistic action of the 
antiserum may depend, in part, on the presence of 
antiamboceptors. Differentiation between the ac- 
tion of anticomplement and antiamboceptor is dif- 
ficult, but it may be accomplished in certain cases 
by appropriate binding experiments. Serum 1, an 
inactive hemolytic serum, i. e., a solution of ambo- 
ceptors and complement oid, is treated with serum 
2. Serum 2 has been obtained by immunization of 
an animal with serum 1, and contains anticomple- 
ment and possibly antiamboceptors. If serum 2 
contains only anticomplement, it will have no ef- 
fect on the amboceptors of serum 1, when the two 
are mixed. The amboceptors are free to sensitize 
corpuscles which may be added, and the latter when 
sensitized undergo hemolysis in the presence of 
complement. If, however, serum 2 contains anti- 
amboceptors, either the cytophilous or the comple- 
mentophilous haptophore of the amboceptor will 
be bound. In either ease, corpuscles which are 
added subsequently would not appear as sensitized, 
for if the cytophilous haptophore had been bound 
by antiamboceptor union between cell receptor and 
amboceptor could not occur; and if the comple- 
mentophilous haptophore had been preoccupied 
complement would have no effect even if the ambo- 
ceptors had united with the cells by their unbound 
cytophilous haptophores. Ehrlich and Morgenroth 
demonstrated such antiamboceptors for certain 
hemolytic serums, and it was their belief that they 
combine with the cytophilous rather than with the 
complementophilous haptophore of the ambo- 
ceptor. However, Ehrlich has recently been able 
to prove the occurrence of an antibody for the com- 



272 INFECTION AND IMMUNITY. 

Danger of plementophilous haptophore in one case. Pfeiffer 
of Antiam- also reports the demonstration of antiamboeeptors 
boceptor. ^ QJ , ^ e S p ec jfi c amboceptors of anticholera serum. 
The possibility of antiamboceptor formation is one 
of practical bearing, in view of the fact that the 
prolonged treatment of a patient with a bacteri- 
cidal sernm may result in the development of such 
antibodies. If present in sufficient amount they 
would combine with new amboceptors which were 
injected and thus deviate the latter from the bac- 
teria. 
Deviation \ phenomenon equally of theoretical and prac- 
ment and tical importance has to do with the so-called devia- 
icai DanI fcion {AbUrikung) of complement. It has been 
ser * found that the action of a bactericidal or liemolvtic 




Fig. 9. — Illustrating deviation of complement. The free 
amboceptors have combined with the available complement, 
and thereby prevented the latter from activating the am- 
boceptors which have united with the bacterial cell. (From 
Xeisser and Wechsberg.) 

serum is lessened, if a great excess of amboceptors 
over complement is added. To explain this fact 
Xeisser and Wechsberg have supposed that when 
so many amboceptors are present that all can not 
be taken up by the cells, those which remain free 
are able to combine with some of the complement 
which is present and thus prevent the accession of 
the latter to the sensitized cells ; that is to say, the 
complement is diverted from its natural direction 
of activity (Fig. 9). This amounts to a protec- 






VENOM HEMOLYSIS. 273 

Hon of the sensitized cells from the action of the 
complement. The phenomenon led Wechsberg to 
suggest that in the therapeutic administration of 
bactericidal serums it may be possible to give too 
much of the serum. Although diversion of com- 
plement is a demonstrated fact, its importance in 
serum therapy is perhaps not definitely settled. 

It is of interest that amboceptors are widely dis- Hemolytic 
tributed in the animal kingdom, and that in cer- ofVenSm!**" 
tain instances they may be demonstrated in the 
secretions. It has long been known that the 
venoms of many serpents have the power of des- 
troying red blood cells. A given venom may 
contain several toxic substances, and the poisons 
.of different serpents by no means coincide in their 
toxic properties. Cobra venom contains two well- 
known toxins, one for the nervous tissue and one 
which dissolves erythrocytes, the neurotoxin having 
the greater pathogenic significance. Cobra venom 
also agglutinates red blood corpuscles, and Flexner 
and Noguchi found that it contains special toxins 
for the cells of various organs (cytotoxins). The 
venom of the rattlesnake, on the other hand, is 
neurotoxic to a less degree, but has a pronounced 
influence in causing capillary hemorrhages. The 
latter power Flexner ascribes to a toxin for 
endothelial cells, which he calls hemorrhagin. 
Through the works both of Flexner and Noguchi 
and of Kyes, facts were learned concerning the 
hemolytic toxin of cobra venom, which may be ot 
great importance in problems of general immun- 
ity. It seems that the hemolysin of venom is an 
amboceptor rather than a toxin of the usual 
nature, and that the aid of complement is neces- 






274 INFECTION AND IMMUNITY. 

sary for its toxic action. The venom itself con- 
tains only the amboceptors, hence the toxicity of 
the substance depends on its being complemented 
after it is introduced into the body. The posses- 
sion of suitable complement, therefore, is a source 
of danger in this instance rather than a means of 
protection for the individual. One may very well 
suspect that a similar relationship is possible in 
connection with other substances which are as yet 
unknown. 
Endocom- A fact of additional importance is that the am- 

pleinentt L 

boceptor finds suitable complement not only in the 
serum of the animal but it may also be activated 
by a complement which the erythrocytes them- 
selves contain. Kyes speaks of the latter as endo- 
complement, i. e., endocellular complement. 
Lecithin In attempting to discover the nature of the com- 
plement which is present in the erythrocytes, vari- 
ous substances existing normally in the red cells, 
as cholesterin and lecithin, were obtained in pure 
form and their activating power for the cobra am- 
boceptors was tested in reagent-glass experiments. 
From this work it was learned that lecithin, a defi- 
nitely known chemical substance, has the activat- 
ing power, and it was, therefore, assumed that the 
endocomplement of erythrocytes is nothing more 
or less than lecithin. All erythrocytes contain 
lecithin, yet not all are equally susceptible to the 
action of venom in the absence of serum comple- 
ment ; that is to say, endocellular lecithin does not 
act as complement with equal readiness in all 
cases. In order to explain this variation it was 
necessary to assume that the lecithin in the cells 
of one animal may be more available as comple- 
ment because it is bound to other cell constituents 



C0BRA-LEGITH1D. 21b 

only in a very loose way, whereas in more resistant 
cells the union is of a firmer nature. 

The relationship between cobra amboceptors and cobra-led- 
lecithin seems to be a very definite one, for Kyes 
was able to obtain a union of the two without the 
intervention of erythrocytes. The resulting sub- 
stance, the cobra-lecithid of Kyes, is a completed 
toxin and needs no further activation. We have 
yet to learn of the true nature of this new com- 
pound, the discovery of which seemed to augur a 
more intimate chemical knowledge of the sub- 
stances which are concerned in immunity. 

According to Bang lecithin itself has no activat- 
ing power for snake venoms. He attributes the 
hemolytic action of the product of the action of 
lecithin on venom according to the Kyes technic 
as due to pre-existant impurities in the lecithin 
That hemolytic substances exist in unpurified 
lecithin there is no doubt. The lecithin used by 
Kyes in his experiments, however, was prepared 
with great precaution to avoid the presence of 
such substances. 

v. Dungern and Coca attribute the action of 
lecithin or venom to a splitting off of hemolytic 
products from the lecithin and fail to obtain an 
"antilecithid" by immunization. They also point 
to a similarity between Kyes elementary analysis 
of the lecithid and that of lecithin and confirm his 
analysis. Their view is supported by Manwaring. 

Kyes, however, had pointed out the fact that 
elementary analysis is, as a general rule, insuffi- 
cient to determine differences in substances con- 
cerned in immune reactions and by a determina- 
tion of molecular weights shows that cobra lecithid 



INFECTION AXD IMMUNITY. 



Hemolysis 

by the Com- 
bined Ac- 
tion of Col- 
loids. 



Neutraliza- 
tion Com- 
plement by 
Salt. 



lias a much larger molecule than lecithin itself. 
His immunization of animals to produce an anti- 
lecithid extended over a much larger period than 
those of v. Dungern and Coea. 

Lecithin is a colloid, and in this connection it is 
interesting to note that it may be used in combina- 
tion with still another colloid in. such manner that 
the hemolysis which they cause is analogous to 
that produced by hemolytic amboceptors and com- 
plements. Landsteiner tried the effect of col- 
loidal silicic acid on erythrocytes which were en- 
tirely freed from serum, with the result that the 
corpuscles were agglutinated under its influence. 
It developed further, however, that colloidal silicic 
acid not only acts as an agglutinin, but also simu- 
lates a hemolytic amboceptor, and in the latter 
capacity it may be activated either by the ordinary 
complement of serum or by lecithin. Hence, we 
have here an instance of the entire cytolytic action 
being performed by two known chemicals, which 
in their action appear to be analogous to ambocep- 
tors and complements. Yet even the action of 
these substances is obscure, for although the chem- 
ical formulae of silicic acid and lecithin are suffi- 
ciently well known, the explanation of their activ- 
ity as colloids is equally obscure with that of the 
albuminous substances. 

Another discovery which tends to bring the 
immune substances into closer touch with pure 
chemistry is that of Hektoen concerning the abil- 
ity of certain salts (calcium chlorid, barium 
chlorid, etc.), to combine with complement in 
such a way that the latter loses its activating and 
combining function in relation to amboceptors. 
This was mentioned incidentally under the sub- 



MATURE OF COMPLEMENT. 277 

ject of antitoxins. The activity of the comple- 
ment is again restored if the inhibiting salts are 
precipitated by suitable chemicals. The salts are 
used in such dilutions that they are largely ionized, 
and Manwaring believes their inhibiting action is 
due to the formation of compounds of the posi- 
tive ions with the complement, resulting in such 
substances as Ca-complement, Ba-complement. 
etc. When the precipitating chemicals are added 
the ions are freed from this combination, as a re- 
sult of which the complement recovers its activat- 
ing properties. It has not as yet been determined 
whether variations in the salts in the fluids of the 
body cause changes in resistance by their action on 
native complements. 

The work of Ferrata, Hans Sachs and Teruuchi, Further An- 
Brand and Hecker has shown that complement complement. 
may be divided into two parts by the separation of 
the albumin and globulin contents of the serum 
containing it. 

Neither of these two parts alone has the power 
to bring about hemolysis in corpuscles previously 
sensitized by the addition of amboceptor. When 
combined, however, hemolysis takes place as before 
separation. 

Absorption of the globulin fraction takes place 
when it is added to sensitized corpuscles, result- 
ing in "Persensitized corpuscles" (Michaelis and 
Skwirsky), which then undergo hemolysis on ad- 
dition of the albumin fraction. The albumin 
fraction, on the contrary, is incapable of being 
bound by the sensitized corpuscles in the absence 
of the globulin fraction. Brand therefore terms 
the globulin fraction as complement "middlepieee" 






27S INFECTION AND IMMUNITY. 

and designates the albumin fraction as comple- 
ment "end-piece." 

The end-piece, middle-piece and amboceptor 
bear the same relation to eacli other as whole 
complement amboceptor and antigen. 

The middle-piece is thermostabile when attached 
to the amboceptor antigen complex, but thermo- 
labile when heated alone or in combination with 
the end-piece. The end-piece is thermolabile. In 
specific complement deviation, it is the middle- 
piece which becomes bound, the end-piece remain- 
ing free. 

Attempts to ascertain the nature of these two 
parts by substitution of lecithin and other lipoids 
have so far been without result in explaining the 
nature of the two components (Liefman and 
Colm). 



CHAPTEE XVII. 



COMPLEMENT DEVIATION. 

In 1901, Bordet and Gengou observed that when 
an antigen was mixed with its specific antibody in 
the presence of complement, the complement was 
fixed or bound and thns rendered unavailable for 
further reactions. This phenomenon has since be- 
come widely known as complement deviation, com- 
plement binding, or complement fixation; and the 
principle underlying it has become of extreme 
value in the determination of the presence of 
substances whose interaction is followed by no 
readily perceptible result such as lysis or precipi- 
tation. 

It will be seen that such a reaction is analogous 
to certain chemical reactions such as the combina- 
tion of ordinary acids and alkalies in which the 
presence of the reaction is determined by the use 
of indicators such as litmus or phenolphthalein. 
Bordet and Gengou used as an indicator a hem- 
olytic system of erythrocytes with their specific 
amboceptor. In this way, for instance, by mixing 
typhoid bacilli with antityphoid serum, incubating 
for a time and then adding erythrocytes sensitized 
with their inactivated antiserum, it was observed 
that hemolysis did not take place. The comple- 
ment in the antityphoid serum had been fixed to 
the typhoid bacilli by the typhoid antibody and 
was thus rendered unavailable for the hemolysis 
of the sensitized erythrocytes, subsequently added. 
Bordet also showed that other indicators such as 



2S0 



INFECTION AND IMMUNITY. 



Non-Specific 
Complement 

In lion. 



a bacteriolytic system could be used instead of 
hemolysis, in order to test for the binding of 
complement. 

Complement deviation obviously belongs to a 
large group of complement inhibition phenomena 
and since some of these have a very close bearing 
on the complement deviation by means of antigen- 
antibody complex it is well to review them. 

Ehrlich and Morgenroth made use of the com- 
plement inhibition of lowered temperature to 
separate complement from amboceptor. 

Hektoen and Euediger found that various ions 
might render complement inactive. Certain sub- 
stances which in themselves are hemolytic have 
been shown to antagonize complement action. 
Among these are to be mentioned bile salts, salts 
of fatty acids, lecithin cholesterin and other lipoid 
bodies. 

Suspensions of finely divided substances have 
been demonstrated to inhibit complement action 
and the assumption that their ability to antagonize 
complement is due to their adsorptive property is 
highly probable. Kaolin, chalk, carbon, sand, etc., 
have been used in this way. 

A wide variety of colloidal substances have been 
shown to inhibit complement; examples of these 
are gelatin, peptone, aleuronat, albumoses, etc. 
Lastly, extracts of bacteria, normal and pathologic 
tissue extracts and the body juices work as com- 
plement inhibitors. 
Anticom- Ehrlich and Bordet by immunizing animals 
of Ehrlich with normal serum succeeded in producing serums 
an or e . j^gjjiy antagonistic to complement action. Accord- 
ing to the Ehrlich conception, these bodies are to 



INHIBITION OF COMPLEMENT. 



281 



be regarded as distinct antibodies, receptors of 
the first order. Moresehi, however, has thrown 
doubt on the existence of such distinct antibodies 
for the reason that in using normal serum as com- 
plement a mixture of protein substances is used 
giving rise, in immunization, to antialbuminous 
bodies which react with the antigen to form com- 
binations which inhibit or bind complement. Such 
combinations in the form of precipitates may be 
demonstrated to act as anticomplements. The 
existence of true anticomplements, therefore, 
while not disproved, has not been satisfactorily 
demonstrated. 

The presence of complementoid in inactivated 
serum may also act as a cause of complement in- 
hibition by occupying the receptors of the anti- 
body. When these various factors which com- 
plicate the complement fixation reaction are con- 
sidered, it will be seen that great care must be 
taken in both the technic and the interpretation of 
results. 

The substance concerned in antigen, antibody 
complement fixation is obtained by processes of 
immunization similar to those concerned in other 
antibodies. In the one case the reaction is fol- 
lowed by perceptible results, in the other by 
fixation of complement. The question arises: are 
the antibodies in these two kinds of reaction iden- 
tical or not? 

That the complement fixation antibody is dis- 
tinct from precipitins and agglutinins is indi- 
cated in different ways. Muir and Martin, by 
immunizing rabbits with guinea-pig serum, ob- 
tained an antibody capable of complement fixation 



Nature of 
Complement 
Deviation 
Antiuotly. 



282 INFECTION AXD IMMUNITY. 

but which contained no precipitin. Moreschi pro- 
duced in fowls antiserum which was high in 
precipitin concentration but did not produce com- 
plement fixation. In like manner the presence of 
antibody complement deviation in the absence of 
agglutinating properties has been noted. In gen- 
eral, complement deviation antibody is destroyed 
at higher temperatures than agglutinins. 

It is in lytic amboceptors that complement fixa- 
tion antibody has its closest analogy and opinions 
are divided as to the identity of the two. Neufeld 
and Haendel regard amboceptor and complement 
fixation antibody as distinct from each other and 
apply the name "Bordet's antibody" to the latter. 
They reach this conclusion from the fact that if 
cholera bacilli and their antiserum are mixed with 
complement and allowed to act at 0° C, hemolytic 
complement is absorbed but not that necessary for 
bacteriolysis. The same mixture allowed to act at 
37° C. results in an inhibition of action of both 
complements. The objection to such a proof lies 
in the fact that the difference may be due to a 
difference in the complements according to Ehrlich 
and his school, who believe in the multiplicity of 
complements. Neufeld and Haendel have also 
immunized animals with a certain water vibrio 
and obtained a serum which was bacteriolytic 
against this vibrio, but not against cholera vibrios. 
Complement deviation, on the other hand, was 
effected by using either of the two micro-organisms 
as antigen. 

If Ehrlich's definition of amboceptor as a sub- 
stance which unites antigen with complement is 
accepted, it is apparent that the term will apply 



VALUATION OF COMPLEMENT DEVIATION 283 

to "Bordet's antibody/' whether it is identical 
with other amboceptors or not. 

It will be readily seen that the reaction of com- Practical 
plement fixation like other immune reactions be- Reaction* 
tween antigen and antibody may be used for the 
identification of either of the two bodies concerned. 

The complement fixation test has been used Biologic Test. 
especially by Neisser and Sachs similarly to the 
precipitin test for the differentiation of proteins. 

Animals are immunized to a certain protein 
and an antiserum is thus obtained. A titration is 
then made with known homologous antigen and 
antibody, in varying quantities, to determine the 
amount of antiserum necessary to produce com- 
plement deviation. The quantity of antiserum 
found by titration to be necessary for complement 
fixation in the presence of homologous antigen, is 
then added to the serum or protein to be tested. 
If this protein and the antiserum are homologous, 
a complement fixation will result. The method 
has been criticized because of its extreme delicacy. 
It is estimated that amounts of protein substances 
will give a complement fixation test which are 
present in one-millionth the quantity required for 
a precipitin test. Uhlenhuth advises the control 
of the method by the precipitin test. Although 
other antigens such as bacteria may be identified 
by complement fixation, the existence of easier 
methods makes complement fixation of little value. 

The existence of easier methods of diagnosis as Antibody 
results in infrequent use being made of the com- 
plement deviation reaction as a means of diagnosis 
in infections with organisms capable of cultiva- 
tion. The presence of the reaction has been 



Test. 






284 INFECTION AXD IMMUNITY. 

demonstrated, however, in a large number of in- 
fections — typhoid, paratyphoid, streptococcus in- 
fections (including streptococcus infections of 
scarlet fever), pneumonia, dysentery, diphtheria, 
etc. 

Ivolle and Wassermann have demonstrated com- 
plement fixation in meningitis and suggest the use 
of the reaction to determine the strength of men- 
ingococcus antiserum. 

Regarding the presence of antituberculin in the 
blood of tuberculous animals and man, conflicting 
results are reported. It would appear that com- 
plement fixation reaction is inconstant during the 
course of tuberculosis and that the reaction occurs 
more constantly after the use of therapeutic in- 
oculations of tuberculin and especially of emul- 
sions of tubercle bacilli. 
Complement It occurred to Wassermann that by using ex- 
in syphilis, tracts of tissues containing antigen, complement 
deviation antibodies might be found in infections 
in which the antigen could not be cultivated. By 
the use of syphilitic tissues he immunized apes 
against s} T philis and by using such syphilitic tissues 
as antigen found complement deviation antibodies 
in the serum of the immunized apes. 

Wassermann, Neisser and Bruck, in 1906, pub- 
lished the results of these experiments together 
with a method adapting them to the serodiagnosis 
of syphilis which has become oommonly known as 
the Wassermann reaction. Since the spirochetes 
of syphilis were known to be found in extreme 
numbers in the liver of the syphilitic fetus, an 
aqueous extract of this organ was used as antigen. 
To this extract was added the inactivated serum 



the Antigen 

of Wasser- 
111:11111, 



WA88EBMANN REACTION. 285 

of the suspected case and after the addition of 
complement, the mixture was incubated an hour. 
Sheep's corpuscles with specific amboceptor were 
then added and the mixture again incubated. In 
case the syphilitic antibody was present, comple- 
ment became bound and no hemolysis took place 
upon second incubation. Through a large number 
of tests the Wassermann reaction has been proved 
to be characteristic for syphilis. 

The idea of Wassermann that the complement Nature of 
binding was due to extract of spirochetes as anti- 
gen and specific amboceptor, soon found opposi- 
tion. Landsteiner, Mtiller and Poetzl, Levaditi 
and others showed by the use of alcoholic extracts 
of normal organs that a substance could be ob- 
tained which acted as antigen and could be 
substituted for the extract of syphilitic liver with- 
out changing the results of the reaction. Finally 
it has been shown that mixtures of lipoid sub- 
stances or crude tissue lecithin could be used as 
antigen. Wassermann pointed out that whereas 
his aqueous extract of syphilitic tissues was ther- 
molabile at boiling, the alcoholic extract of normal 
organs was thermostabile : further that the aqueous 
extracts of normal organs do not act as substitutes 
for aqueous extracts of syphilitic organs. He 
therefore regarded his original ideas as to the 
specificity of antigen as correct and held that 
aqueous extract of syphilitic liver was the only 
extract which could be used without chance for 
error. 

Seligmann and Pinkus have made a study of 
the various extracts and conclude that the differ- 
ence in heating aqueous and alcoholic extracts is 



IXFECTIOX AXD IMMUNITY. 






due to the fact that in the aqueous extracts, a 
large amount of protein is present with the lipoids 
on which the antigenic action depends, and that 
these lipoids become bound to the protein through 
heating; further, they believe that these lipoid 
substances may be extracted with water in syph- 
ilitic liver because through degenerative processes 
they become split off, while in normal organs they 
must be split off by alcohol and heat. 

They conclude that the antigen is therefore of 
non-specific lipoid nature and that it acts as 
activating the complement binding property of 
syphilitic sennn. 

The nature of the substance in the serum of 
syphilitica which in combination with antigen 
inhibits complement action, is still unknown. 
Xoguchi has shown that it begins to show the 
effects of heat at 45° C. At 56° C. it is somewhat 
diminished in activity and at 62° C, its activity 
is lost. It has been thought of as an antibody 
because of its development with the development 
of the disease and its disappearance with the cure 
by specific treatment. 

As was stated in the beginning of the chapter, 
the various materials used in complement devia- 
tion may of themselves have anticomplementary 
properties. In addition, it might be stated that 
extracts of organs may also have a hemolytic 
action. The importance of quantitative relations 
and contral experiments will therefore be appar- 
ent. The Noguchi modification of Wassermann's 
method has given satisfactory results in a large 
number of cases. The preparation of materials 



TECHNIC OF WASSERMANN REACTION. 287 

required for the test will be described and then 
their application to the test. 

Sheep's corpuscles may be obtained from the 
jugular vein of the. animal. The blood is defibri- 
nated and washed by centrifugation with salt 
solution, the salt solution being changed twice. 
A 5 per cent, suspension of these corpuscles in 
0.85 per cent, salt solution is used for the test. 

Inactivated hemolytic serum for sheep's cor- 
puscles is prepared by immunizing a rabbit against 
sheep's corpuscles. The animals should be injected 
intraperitoneally with washed corpuscles made up 
to the volume of blood from which they were 
taken, by the addition of salt solution. At least 
four or five injections should be given at intervals 
of from four days to a week, and with amounts 
beginning with 2 c.c. and ending with from 12 to 
20 c.c. The animal should not be bled before ten 
days after the last injection. Blood is obtained 
from the marginal vein of the ear and allowed to 
clot. The serum is then removed, heated to 56° 
C. for one-half hour and standardized as follows : 
Varying graded amounts of the inactivated serum 
plus 0.1 c.c. of complement (fresh guinea-pig 
serum, best obtained by aspiration from the heart), 
are added to each of a number of tubes containing 
1 c.c. of 5 per cent, sheep's corpuscle suspension. 
The tubes are incubated for one hour and that tube 
noted in which the smallest amount of amboceptor 
(inactivated rabbit's serum), produced complete 
•hemolysis. This is called the hemolytic unit of 
amboceptor. 

The antigen is prepared by the extraction of 
minced syphilitic or normal liver, with 10 volumes 



288 INFECTION AXD IMMUNITY. 

of 95 per cent, alcohol for a week at 37° C. This 
extract is filtered and evaporated by means of a 
fan at a temperature below 40° C. The residue 
is extracted with ether and the ether evaporated. 
This residue is again taken up in ether and frac- 
tionated twice with acetone to remove the acetone- 
soluble hemolytic substances. The acetone-insol- 
uble residue is evaporated to dryness and extracted 
with 95 per cent, alcohol. This solution is used 
as a stock antigen and suspensions in salt solution 
are used as material for tests. 

A titration of antigen should then be carried 
out as follows: A serum from a known case of 
syphilis should be obtained and 0.1 c.c. of the 
inactivated serum added to each of a series of 
tubes. Another series of controls is made by the 
use of a like quantity of inactivated norma] serum. 
To each of the tubes of the test series graded 
varying amounts of antigen are added and like 
amounts added to the control tubes. Complement 
0.1 c.c. is added to each of all of the tubes and 
the set incubated one hour. At the end of this 
time, two units of amboceptor for sheep's cor- 
puscles and 1 c.c. of 5 per cent, suspension of 
sheep's corpuscles are added and the tubes incu- 
bated for another hour. The smallest amount of 
antigen which, with the syphilitic serum, will bind 
complement, is indicated by the tube containing 
the lowest quantity of antigen in which hemolysis 
has not taken place. The control tube containing 
a like quantity of antigen but with normal serum 
should be completely hemolyzed. 

Having now standardized both antigen and 
hemolytic amboceptor, the test of the serum in 



TECHNIC OF WASSERMANN REACTION. 289 

question is carried out as follows : 0.1 c.c. of 
inactivated serum to be tested is added to 0.1 c.c. 
of complement and that amount of antigen added 
which was found to be the minimum required to 
bind complement in the presence of 0.1 c.c. of 
syphilitic serum. Control tubes are made as fol- 
lows: One positive control is made as the test 
serum tube but with a like quantity of inactivated 
known syphilitic serum in place of the serum to be 
tested. One negative control is prepared with the 
same components as the test serum tube except 
that inactivated normal serum is used instead of 
the serum to be tested. Three control tubes are 
made with the test serum in one, positive serum in 
a second and the normal serum in the third, and 
salt solution substituted for the antigen to ascer- 
tain whether or not the serum alone causes com- 
plement deviation. One control tube is made with 
salt solution instead of serum to see if antigen 
alone will bind complement. Another control may 
be made with complement, human serum to be 
tested and corpuscles to exclude hemolysins for 
sheep's corpuscles being present in the human 
serum. After incubation of the antigen, comple- 
ment, serum mixtures and control tubes for one 
hour, the hemolytic system, consisting of two 
units of hemolytic amboceptor and 1 c.c. of 5 per 
cent, corpuscle suspension, is added to each tube. 
After a second incubation of one hour the tubes 
are examined for hemolysis. There should be no 
hemolysis in the positive control tube. In the 
other control tubes complete hemolysis should have 
taken place. If hemolysis is present in the tube 
containing the test mixture the reaction is nega- 






290 INFECTION AND IMMUNITY. 

ti\e, that is, there is no evidence of .syphilis. If 
hemolysis is absent as in the positive control tube 
the reaction is characteristic of syphilis. 

Various modifications of this technic have been 
used by different cxperimentors with good results. 
NoguchL, for instance, has used human blood sus- 
pensions with their amboceptor instead of sheep's 
blood, the purpose being to avoid complications 
due to hemolysins for sheep's corpuscles found 
occasionally in human serum. It has been found 
that a larger number of positive reactions in 
syphilis can be obtained by using non-heated 
serum of the suspected patient. It is also found, 
however, that a larger number of normal inactive 
serums react as positives; the reaction is therefore 
not so specific as when the heated serum is used. 
Synthetical antigens composed of mixtures of 
lipoid bodies of known composition, have been used 
with varying degrees of success. 
value of the The Wassermann reaction has proved to be of 
AVassermun^ g re at value in the diagnosis of syphilis. The per- 
centage of positive reactions found in the various 
stages of syphilis varies with the technic of differ- 
ent observers. The following table is made from 
a collection of percentages by Pearce : 

Highest Lowest 

Stage of Disease per cent, per cent. 

Trimary syphilis 92.8 64.4 

Secondary syphilis 100 71 

Tertiary syphilis 100 63 

Early latent syphilis 76 51 

Late latent syphilis 79 46 

Hereditary syphilis 100 86 

The percentage of cases in which syphilis could 
be excluded so far as possible from history and 



WASSERMANN REACTION. 291 

negative clinical symptoms, and which gave a 
positive reaction, varies from 0.3 to 3.6 per cent. 

The results in the parasyphilitic diseases are as 
follows : In tabes, using blood serum, the average 
of positive reactions is 62.88 per cent.; using 
cerebrospinal fluid. 56.2 per cent. In general 
paresis, using blood serum, 88.1 per cent, of cases 
are positive, with cerebrospinal fluid 90 per cent. 
(ISToguchi). 

The earliest appearance of the Wassermann re- 
action is that reported by Lesser, eight days after 
exposure. The reaction usually appears by the 
end of the fourth week after the appearance of the 
chancre. 

Among non-syphilitic diseases the Wassermann 
reaction has been observed in trypanosomiasis, in 
leprosy with less constancy, in scarlet fever (usu- 
ally weakly positive and transient), in frambesia, 
tuberculosis and carcinoma. In these non-syph- 
ilitic diseases, the ones giving the highest per 
cent, positive reactions are those least likely to be 
confused with sy^philis. The reactions found at 
times in carcinoma and tuberculosis may be due 
to concurrent syphilis. 

Specific treatment has been found by all ob- 
servers to have a profound influence on the 
Wassermann reaction and disappearance of the 
test has been observed after treatment for from 
six months to five } T ears. 

A positive reaction is therefore regarded by 
many observers as an indication for further 
treatment. 



CHAPTER XVIII. 



CYTOTOXICS. 



Cytotoxin or 



Following the discovery of immune hemolytic 
serums it was a short step to experiments which 
involved immunization with various other tissue 
cells, and as a result of such work we are to-day 
familiar with antiserums for almost every organ 
of the body. 

Metchnikoff gave the name of cytotoxins to those 
cytoiV-siii. scrums which destroy cells other than bacteria 
and erythrocytes; the word cytolysin is used syn- 
onymously. Naturally a serum which destroys any 
cell whatsoever is cytotoxic, but according to the 
rather loose custom which prevails, we speak of 
bacteriolysins, hemolysins and other cytolysins, in- 
cluding among the latter serums which destroy 
leucocytes, the cells of the liver, kidney and other 
organs. 

Cytotoxins are of interest, not only because they 
utnYty of are produced in accordance with the general 
ytotoxms. j awg Q £ an ti_tj 0( jy formation, but they have, in ad- 
dition, a certain theoretical and perhaps practical 
importance. Immediately on their discovery the 
possibility became manifest that they might be 
utilized in the elucidation of certain physiologic 
and pathologic problems. For example, by put- 
ting the thyroid out of function through in- 
jections of thyrotoxic serum it might be pos- 
sible to confirm, or to prove incorrect, cer- 
tain theories as to the role of the gland in 
metabolism. Or, by the selective destruction of a 
tissue, facts concerning its regenerative powers 



Theoretical 



SPECIFICITY OF CYTOTOXICS. 293 

might be learned. The use of an antipancreatic 
serum might throw some light on the nature of 
diabetes. Therapeutic possibilities also suggested 
themselves. One might be able by means of artifi- 
cial anticytotoxic serums to counteract cytotoxins 
which were being formed pathologically in the 
body. Or, by injecting small amounts of a cyto- 
toxic perhaps one could stimulate to a renewed 
production of the homologous cells ; small doses of 
a hemolytic serum might be useful in combating 
anemias. Or small amounts of leucotoxic serum 
might cause an increase in the number of leuco- 
cytes, and thereby an increased resistance to infec- 
tion. Perhaps autocytotoxins are formed in some 
such manner as the following: An extraneous 
toxic substance causes the destruction of a few 
kidney cells, the constituents of the latter reach 
the circulation and stimulate other organs to the 
formation of autonephrotoxic amboceptors, which 
then assist in the destruction of more renal tissue, 
with the result that a vicious cycle is set up. 

In spite of so many theoretical values, the study g a ^ificity. 
of cytotoxic serums has not yielded the results 
which were anticipated, perhaps chiefly because of 
their lack of specificity (Pearce and others). Al- 
though the cells of the different organs differ wide- 
ly in their morphology and function, there are no 
doubt certain chemical constituents (receptors) 
which they possess in common. Of this we have 
experimental proof from the fact that immuniza- 
tion with one type of cell yields a serum which is 
toxic for the cells of various organs. It is difficult 
or impossible to injure one organ to the exclusion 
of all others by means of a cytotoxin. One may 
attempt to purify a cytotoxic serum through ab- 



294 



1XFECTI0X AND IMMUNITY. 



Determina- 
tion of Cyto- 
toxic Action. 



Technic of 

Immunization 



sorption of the adventitious amboceptors by means 
of the corresponding cells. Inasmuch, however, as 
the result is a decrease in the chief amboceptors 
as well as of the adventitious, the desired object is 
not fully realized. Theoretically the cytotoxic 
treatment of malignant tumors offers an impor- 
tant field for research. But here, too, various dif- 
ficulties are involved, as lack of specificity of 
serums and the multiplicity of cell-types which 
constitute different tumors. 

Experiments with cytotoxic serums may be con- 
ducted in vitro or in the living animal. In either 
case a necessary condition for the recognition of 
the cytotoxic action is the presence of some dis- 
tinctive sign of vitality on the part of the cell, the 
loss of which may be taken as evidence of cell- 
death. Loss of motility and of proliferative power 
indicate the death of bacteria, and solution of 
hemoglobin the death of erythrocytes. Under par- 
ticular conditions loss of motility on the part of 
certain tissue cells, as spermatozoa, leucocytes and 
ciliated epithelium, is an evidence of cell death or 
cell injury. The toxic action of serums on cells of 
fixed form is more difficult to determine, and for 
evidence one must rely on such points as clearing 
of the protoplasm (digestion?), swelling of the 
cell and nucleus, actual solution of the cytoplasm, 
or degenerations of the homologous organs when 
the serum is injected into the living animal. 

The technic of immunization with tissue cells is 
similar to that of immunization with bacteria. In 
order to obtain leucocytes in abundance, artificial 
leucocytosis is produced in the peritoneal or pleural 
cavity by the injection of bouillon, or l}miph 



SPERMOTOXIN. 295 

glands, spleen or bone-marrow may be ground up 
and injected. 

Immunization with solid organs, as liver, kidney 
or testicle, is easily accomplished, a necessary pre- 
liminary for injection being a thorough disintegra- 
tion of the tissue by grinding with sterile sand; 
the resulting mass when suspended in salt solution 
passes through the injecting needle readily. 

Cytotoxins, like bacteriolysins and hemolysins, Aml>oce ptors, 
are complex substances, in that they consist of am- complements 

1 ' J and Anticyto- 

boceptors and complements. The amboceptors toxins. 
alone are increased during immunization, the com- 
plement being a normal constituent of the serum 
of the animal. The phenomena of inactivation 
and reactivation are observable here as in connec- 
tion with other cytolytic serums. Anticytotoxins 
are readily produced by immunization with many 
cytotoxins; the antiserum usually consists of anti- 
complement, but in some instances antiambocep- 
tors have been described. 

Simultaneously, or nearly so, Landsteiner in spermotoxin. 
Vienna and Metchnikoff in Paris reported the 
production of spermotoxic serums by immuniza- 
tion with spermatozoa, the natural motility of 
which rendered the recognition of cell death easy. 
The technic which Landsteiner first employed was 
that of the Pfeiffer experiment in that he immun- 
ized guinea-pigs with the spermatozoa of cattle and 
observed loss of motility on the part of the cells 
when they were injected into the peritoneal cavity 
of the immunized animals. Comparable with 
many other cytotoxins, spermotoxin kills the ho- 
mologous cell without causing its solution. The 
loss of motility is also observed in hanging-drop 
preparations provided a fresh or a complemented 



296 INFECTION AXD IMMUNITY. 

serum is used. Most normal serums show a 
greater or less degree of toxic action for the sper- 
matozoa of other animals, and normal spermotox- 
ins like the immune consist of amboceptor and 
complement. Metchnikoff claims to have pro- 
duced an autospermotoxin by immunizing guinea- 
pigs with the spermatozoa of other guinea-pigs. 

When a spermotoxic serum is injected into the 
living animal it is thought that the amboceptors 
are taken up by the homologous cells, and this 
would seem to affect the vitality of the sperma- 
tozoa, inasmuch as De Leslie rendered male mice 
sterile for 16 to 20 days by the injection of the 
serum. 

It is of theoretical interest that castrated ani- 
mals will yield spermotoxin by immunization, 
showing that the amboceptors are not of necessity 
produced by the analogous tissue of the immun- 
ized animal. From the fact that spermotoxic 
serums are hemolytic, it is assumed that certain 
receptors are common to erythrocytes and sperma- 
tozoa. Hemolytic serums, on the other hand, may 
not be spermotoxic. There is nothing contradic- 
tory in this lack of reciprocal action, for those re- 
ceptors which are common to the two cells may not 
be important for the life of the spermatozoon, 
whereas the opposite condition prevails with the 
erythrocyte. 

It is certainly of interest that immunization with 
the plasma of ova causes the formation of spermo- 
toxic amboceptors, a fact which points to certain 
common constituents of the two cells. 

Antispermotoxin may be produced by immuniza- 
tion with spermotoxic serum (anticomplement or 
anti amboceptor). 



LEUCOTOXIXS. 297 

Following technic similar to that employed by cytotoxin 
Landsteiner, von Dnngern obtained a cytotoxic j^pitneiAJm'! 
serum for ciliated epithelium of the trachea. The 
cells disintegrated in the peritoneal cavity of the 
immunized animal, but not in that of the normal 
animal. This serum also proved to be hemolytic 
in spite of the fact that no erythrocytes were in- 
cluded in the injections. That the receptors which 
characterize ciliated epithelium are widely distrib- 
uted is shown by the fact that immunization with 
cow's milk causes the formation of a cytolytic 
serum for the tracheal epithelium of the cow. 

Leucotoxic, lymphotoxic or lymphatotoxic 
serums are prepared by immunization with ex- 
udates which are rich in leucocytes, or with the 
emulsions of lymphoid organs: lymph glands,, 
spleen, bone marrow. Metchnikoff prepared the 
first serum of this nature by the injection of the 
spleen of rats into guinea-pigs. Leucotoxic serums 
are toxic, not only for leucocytes, but also for red 
corpuscles and endothelial cells. When injected 
into the peritoneal cavity the endothelium is 
thrown off, and when given subcutaneously the 
capillary endothelium is attacked, with the result 
that blood escapes to form a large hematoma. The 
action of the serum on leucocytes may be observed 
in vitro. The mononuclear cell's are often more 
susceptible than the polymorphonuclears, although 
this depends somewhat on the animals and the 
particular organ used for immunization. The cells 
lose their motility, the cytoplasm becomes trans- 
parent, and swells to form a large clear vesicle, 
which appears to be surrounded by a sharp, thin 
membrane. The cell contents may be discharged 
or entirely liquefied, the nucleus alone being rec- 






298 INFECTION A\D IMMUNITY. 

ognizable. Leucocytes are agglutinated by the 
serum. A strong leucotoxic serum may be fatal 
to the animal when injected into the peritoneal 
cavity or blood stream, the exact cause of death 
being obscure. 
oid Age. Metchnikoff, taking the view that the phenom- 
ena of old age depend on the destruction of vari- 
ous tissue cells by the mononuclear leucocytes 
(macrophages), expressed the hope that a lympho- 
toxic serum might be utilized to combat the action 
of these cells with the result that life would be 
prolonged. Whether or not his view as to the 
cause of old age is correct, his plan of antagonizing 
it had to be abandoned because leucotoxic serums 
do not injure the macrophages to the exclusion of 
other leucocytes. 
•Effect of The injection of a leucotoxic serum into the per- 
sernm U on t( Re- itoneal cavity of a guinea-pig causes a temporary 
! V*t ane . e of decrease in the number of leucocytes, and during 

Infections. . - 

this period of hypoleucocytosis the resistance of the 
animal to peritoneal infections with the organisms 
of t} r phoid and cholera is lowered. One may refer 
this effect to the destructive action of the serum 
on the leucocytes, by which phagocytosis is pre- 
vented, or, according to Wassermann, it may de- 
pend on the action of anticomplement which the 
leucotoxic serum contains. (Leucocytes contain 
complement, hence immunization with leucocytes 
causes the formation of anticomplement.) It is 
probable that both factors are of influence. In the 
course of from twenty-four to forty-eight hours 
after peritoneal injection of the serum, the leuco- 
cytes reaccumulate to an enormous extent. Dur- 
ing this secondary Iryperleucocytosis resistance to 
peritoneal cholera or typhoid is increased. Some 






NEPHROTOXIC 8. 



299 



Nephrotoxic 

Sernm. 



non-toxic substances, as bouillon, have a similar 
effect, and although the secondary leucocytosis is 
never so great as that caused by the leucotoxic 
serum, the protective action is equally high-. It 
would seem that, leucocyte for leucocyte, those 
which accumulate following the injection of leuco- 
cytoxic serum are less efficient in antibacterial 
action than those whose presence is caused by 
nontoxic substances (Eicketts). Hence there prob- 
ably is no field for leucotoxic serum as a means of 
temporarily increasing resistance to bacterial in- 
fections. 

By guarded immunization Besredka obtained an 
antileucotoxic serum. 

Nephrotoxic serums have been brought into 
close relationship with clinical and anatomic prob- 
lems by a number of investigators. Some normal 
serums are held to be nephrotoxic inasmuch as 
their injection is followed by albuminuria and 
renal degenerations. Immune nephrotoxins have 
a similar but more pronounced effect, and Linde- 
man referred the death of his experiment animals 
to the development of a uremic condition. Of 
more than ordinary interest is the claim of cer- 
tain workers that autonephrotoxins may be formed Antinephro- 
in the body. One (Lindeman) caused a toxic 
nephritis in dogs by the injection of potassium- 
bichromate. The serum of this dog, although free 
from chromic acid, was toxic for other dogs, pro- 
ducing the symptoms which are caused by an im- 
mune nephrotoxic serum. It was supposed that 
the chromic acid in the fir*st dog caused disintegra- 
tion of renal cells and that the constituents of the 
latter were then taken up by nephrotoxic receptors 
which normally reside in the organs of the ani- 



300 INFECTION AND IMMUNITY. 

mal; as a result the receptors were overproduced 
and their presence became manifest when the 
serum was injected into other dogs. In accord- 
ance with this view the original toxic cause of a 
degenerative nephritis would be of less conse- 
quence for the continuance of the condition than 
the formation of the nephrotoxic amboceptors ; i. e., 
the formation of an autonephrotoxin. 

Somewhat similar results were obtained by oth- 
ers through ligation of the renal vein or artery on 
one side. Constituents of cells of the isolated kid- 
ney were supposed to be absorbed, and as a conse- 
quence nephrotoxic amboceptors were produced in 
excess by organs of uncertain identity. To the 
action of the new-formed bodies were attributed 
the degenerative changes which were found in the 
opposite kidney, and the nephrotoxic properties 
which the serum manifeested when injected into a 
healthy animal of the same species. 
Antinepiiro- According to Ascoli and Figari unilateral neph- 
< H 3 > i "ert'ropi i »y C rec t° mv so injures the opposite kidney (overwork) 
that the serum of the animal becomes nephrotoxic. 
They state also that an animal, the serum of which 
contains nephrotoxin, may antagonize the latter 
by the production of antinephrotoxin, and suggest 
that spontaneous recovery from nephritis may be 
due to the action of such an antibody. They would 
account for the cardiac hypertrophy of nephritis 
by the action of nephrotoxic serum in causing con- 
traction of the peripheral vessels with consequent 
increase of blood pressure; and for the nervous 
symptoms on the basis that the serum contains a 
neurotoxic constituent. 

We hardly dare consider such far-reaching con- 
clusions as decisive until they have been extensively 



OTHER CYTOTOXICS. 



301 



Neurotoxins. 



confirmed. Yet whatever may be their real value 
they serve to emphasize the possibility that those 
principles which are so important in relation to 
immunity against infectious diseases, may be 
equally important in relation to other pathologic 
conditions. 

Hepatotoxins have been obtained by a number Heimto 
of workers, and the attempt has been made to pro- toxins - 
duce autohepatotoxins by injecting liver tissue of 
the guinea-pig into animals of the same species. 
The success was not unqualified. Hepatotoxins 
when injected are reported to cause insular degen- 
erations of the liver; however, the lesions may be 
caused, in part at least, by capillary emboli of en- 
dothelial cells or erythrocytes. 

Neurotoxic serums have been studied with some 
thoroughness. Whether one injects the cerebrum, 
cerebellum or spinal cord, the resulting serums 
apparently are similar; either an anticerebral or 
an anticerebellar serum will cause degenerations 
of the spinal ganglion cells. In view of their 
broad range of action it seems improbable that 
neurotoxic serums will be of service in clearing up 
the etiology of system degenerations of the nervou's 
tracts. They are usually hemolytic and hemag- 
glutinating and may also be endotheliotoxic and 
leucotoxic. When mixed with emulsions of the 
homologous brain tissue the neurotoxic ambocep- 
tors are bound by the receptors of the nervous tis- 
sue, and the serum consequently loses its toxicity. 
Antineurotoxic serums have been described. 

Sync3^tiolysin is the name given to a serum which 
is obtained by immunization with the placenta. 
Certain writers (Veit and Scholten, Charrin and Eclam » sia - 
Delamare) report that the injection of placentar 



Cyiicytio- 
toxin in Re- 
lation to 



302 INFECTION AND IMMUNITY. 

tissue alone causes albuminuria, a consideration 
which led them to assume that the placentar cells 
contain a nephrotoxic substance. Inasmuch as 
placentar cells or their constituents ma}' reach the 
circulation during eclampsia (Schmorl) it was 
not a long step to suppose that the nephritis of 
pregnancy is due to the toxic syncytial cells which 
are absorbed. The results which Weichardt re- 
ported gave some strength to the view just cited. 
By treating placentar tissue of rabbits with the 
specific cyncytiolysin the toxin supposedly was lib- 
erated, and the mass when injected into normal 
rabbits is said to have produced symptoms of an 
eclamptic nature. On the basis of these observa- 
tions the hope has been expressed that an anti- 
toxin for eclampsia might be prepared by immun- 
ization with placentar tissue. However, the con- 
ditions are by no means simple; any value which 
the destruction of circulating syncytial cells or 
their toxin would afford might be more than offset 
by the action of the hemotoxin and neurotoxin 
which the serum is said to contain. Whether or 
not the hypothetical toxin of syncytial cells may 
be separated from the other cell constituents, and 
whether immunization with the toxin will yield 
an antitoxic serum are possibilities which remain 
for further investigation; the results cited have 
not been obtained by all observers. 

Liepmann hopes for a serum-diagnosis of preg- 
nancy. If, as supposed, the blood of a pregnant 
woman contains syncitial cells or their products 
of degeneration, the serum when mixed with 
a specific syncytiolysin may cause a precipitate. 
He claims to have demonstrated the presence of 



NUCLEOPROTEID IMMUNIZATION. 303 

placentar constituents in the circulation by this 
biologic method. 

Antithyroid serum is prepared by immuniza- Thyrotoxic 
tion with ground-up thyroid tissue or with extracts 
of the organ.' It is hemolytic, even though all the 
blood has been washed from the tissue which was 
injected. Portis immunized with the "colloid" 
material of the gland obtaining a hemolytic thyro- 
toxic serum. When injected into the living animal 
degenerative changes are produced in the thyroid, 
and some authors report the tetanic phenomena 
which often follow surgical removal of the thyroid. 
In very careful work, however, Portis could not 
produce "the exact picture presented by thyrodec- 
tomized animals." Degenerative changes were 
found in various organs, as liver, spleen and kid- 
neys. 

With the idea of preparing an antigen which 
would contain, so far as possible, only substances 
characteristic of variety of cells used, Beebe has 
made use of nucleuproteids of various organs, espe- 
cially thyroid gland, to produce antiserums. His 
results would indicate that in this way serums may 
be obtained, which are specific for different vari- 
eties of cells except in high concentration. 

With the use of such a thyrotoxic serum he has 
reported good results in cases of hyperthyroidism. 

Pearce has failed to confirm these results and 
obtains results, with neucleoproteid as antigen, 
which are similar to those which he obtained with 
simple extracts. 

Beebe, however, criticises the technic of Pearce 
in that Pearce heated his preparation, thus, accord- 
ing to Beebe, destroying the specific biologic char- 
acter of the extract. 



INFECTION AND IMMUNITY. 



Sympathetic 

Ophthalmia. 



Pancreo toxin. 



Other 
Cytotoxins. 



Toxin of 

Exhaustion. 



It would appear that further observations are 
desirable before conclusions can be drawn regard- 
ing the value of nucleoproteid as antigen. 

Brown Pusey has made the interesting sugges- 
tion in regard to sympathetic ophthalmia that the 
disease may be due to the formation of autocyto- 
toxins which are specific for the cells of the inner 
surface of the ciliary body and iris. The disinte- 
gration products of the corresponding cells in the 
eye which was primarily injured would constitute 
the stimulus to the formation of the specific anti- 
bodies. The possibility is as yet a problematic 
one. 

The experimental study of cytotoxic serums for 
the pancreas has, up to the present time, thrown 
little light on pancreatic diseases. It stated that 
the serum may cause transient glycosuria, and it 
is said to have an antitryptic action in experiments 
performed in the test-glass. 

The results of different observers concerning the 
action of antiserums for the adrenal gland are not 
in entire accord. Although degenerative changes 
may be caused in the gland when the serum is in- 
jected, the action is not specific; the serum may 
be highly hemolytic (Abbott). 

Ceni claims to have demonstrated in the circula- 
tion of epileptics a cytotoxin which causes the ep- 
ileptic attacks, and reports the production of a 
specific antitoxin. 

Weichardt has published descriptions of a toxin 
which is peculiar to states of exhaustion, giving 
an account of the specific antitoxin which he pro- 
duced by immunization. 

Other cytotoxins which have been prepared, as 
those for the pituitary body, gastric mucosa and 






AUTOCYTOTOXINS. 305 

cardiac muscle, have at the present time nothing 
more than general biological interest. 

It would seem that no question in relation to Concerning 
cytotoxic serums is more important than the pos- toxinsT* " 
sibility that autocytotoxins may develop and in- 
stitute the vicious cycle which was mentioned ear- 
lier. It is true that the results of some investiga- 
tors suggest the probability of such a process, but 
it would be going too far to say that its existence 
as an important pathologic law has been estab- 
lished. On the contrary, the development of auto- 
cytotoxins is one of the rarest of occurrences in 
experimental work; and Ehrlich has spoken of 
the inability of the body to form such antibodies 
as a condition of "horror autotoxicus." The cells 
of our kidneys and our erythrocytes certainly do 
degenerate, and it is quite possible that the recep- 
tors which are thereby liberated actually reach 
cytotoxic amboceptors which are situated in other "Horror 
organs. In the event that the process extends to 
this point, Ehrlich assumes that the amboceptors 
are of a sessile nature, that in spite of the stimula- 
tion to which the cells are subjected the "sessile 
amboceptors" may not be overproduced and lib- 
erated as in the case of antibodies for bacterial 
substances or for the cells of other species. In 
accordance with this explanation we are saved 
from intoxications of the nature in question be- 
cause of the sessile nature of the cytotoxic ambo- 
ceptors. 



CHAPTER XIX. 



PHAGOCYTOSIS. 

As one may learn from the writings of Metchni- 
koff, phagocytosis, in its broad sense, exercises 
three distinct functions: nutritional, resorptive 
and protective. 
Phagocytosis Phagocj^osis, for purposes of nutrition, is most 
of Nutrition, highly developed in unicellular ameboid organ- 
isms, but is found also in animals of considerable 
organic differentiation. It is, perhaps, nowhere 
more striking than among certain myxomycetes, 
which are large, naked, multinucleated, protoplas- 
mic masses belonging to the plant kingdom, and 
which possess a peculiar, slow, undulating motility. 
Ingestion is accomplished through protoplasmic 
arms (pseudopodia) which are thrown out to en- 
velop the object. Minute plant and animal cells, 
living or dead, are ingested in this manner by the 
myxomycetes, amebse and other unicellular organ- 
isms and are subsequently digested by means of 
intracellular ferments. The ferments which have 
been extracted from such cells are proteolytic since 
they digest gelatin and fibrin, usually in an acid 
but sometimes in an alkaline medium; that from 
ameba? has been called amibodiastase. In the proc- 
ess of digestion a "vacuole," acid in reaction and 
containing the ferment, forms around the in- 
gested particle. In certain phagocytic unicellular 
organisms the protoplasm shows a degree of differ- 
entiation, a mouth and an anus being simulated at 
points where the food is most readily taken in and 
discharged. Instances are cited in which ameboid 



CHEMOTAXIS. 307 

organisms protect themselves against inimical cells 
by ingesting, killing, and finally discharging or 
digesting the latter. 

The botanist, Pfeiffer, first described the phe- chemotaxis. 
nomena of negative and positive chemotaxis in re- 
lation to the myxomycetes. Under certain condi- 
tions they either are attracted toward or move 
from moist places. That a negative chemotaxis 
may be changed into a positive was shown in rela- 
tion to salt solutions. When placed in the vicinity 
of or in contact with strong solutions the cell re- 
cedes, whereas if one passes gradually from weaker 
to stronger solutions the latter eventually attract 
rather than repel the cell. 

As one goes higher in the animal scale intracel- intestinal 
hilar digestion for purposes of nutrition is con- 
fined to rather definite groups of cells. The intes- 
tinal epithelium of certain invertebrates consists 
of "sessile phagocytes," cells which, individually 
or after fusion into plasmodial masses, surround 
and digest solid particles of food. It is said that 
in sponges the digestive tract is not sharply sepa- 
rated from the mesodermal tissue, and the cells of 
the latter share with the former the function of 
intracellular digestion. 

In higher invertebrates and in all vertebrates 
the intestinal epithelium ceases to be essentially 
phagocytic, digestion being accomplished rather by 
ferments which have been secreted by the intestinal 
and related glandular epithelium. Such animals, 
nevertheless, possess an abundance of phagocytic 
cells, but they are in the main mesoblastic in na- 
ture, and may have nothing more than a remote 
relationship to the nutrition of the organism. 



30S INFECTION AND IMMUNITY. 

Macrophages Metchnikoff divides the phagocytic cells of ver- 
an phages" tebrates into the macrophages and the miero- 
phages. The macrophages or large phagocytes in- 
clude the large lymphocytes, endothelial cells, 
ameboid connective tissue cells and others which 
may occasionally take up foreign particles. Our 
polymorphonuclear leucocytes are the micro- 
phages. In relation to immunity we are concerned 
chiefly with the large lymphocytes (macrophages), 
and the polymorphonuclear leucocytes (micro- 
phages). Although such cells may contain many 
ferments, Metchnikoff recognizes but one type in 
relation to their resorptive, digestive and bacteri- 
cidal activities. This he calls cytase and distin- 
guishes that of the macrophage as macrocytase and 
cytases. that of the microphage as microcytase. Cytase 
corresponds to the complement of Ehrlich. The 
two cells do not have identical activities, the ma- 
crophage being concerned specially in the resorp- 
tion of tissue cells and in immunity to certain 
chronic diseases, as tuberculosis and leprosy, 
whereas the microphage is the cell which is con- 
spicuously antimicrobic in relation to acute infec- 
tions. 

Resorption of According to Metchnikoff, the leucocytes are 
very active in the resorption of useless or foreign 
cells. During the metamorphosis of certain in- 
vertebrates it is said that the larval tissues are 
englobed and digested by wandering pha- 
gocytic cells. In involution of the uterus 
the muscular tissue is invaded by leuco- 
cytes which take up and digest or carry away tht 
"retrogressive elements." MetchnikofFs concep- 
tion of certain atrophic processes, particularly 



Xative Cells. 



PHAGOCYTES AND RESORPTION. 309 

those which are grouped among the senile atro- 
phies, is of interest to pathologists. In sclerotic 
atrophy of the ovaries the large lymphoc3'tes in- 
vade the tissue, surround and destroy the ova and 
follicular epithelium and eventually, as fibroblasts, 
participate in the formation of fibrous tissue which 
to a degree is substituted for the original struc- 
ture. In old individuals or in* those of failing 
mentality it is said that ganglionic cells are found 
in a greater or less degree of atrophy because of 
the action of certain mononuclear phagocytes 
(neuronophages) which are contiguous to or form 
a zone around the cell. The neuronophages may 
represent mononuclear cells from the blood or 
those of proliferated neurogliar tissue. The best The wiiiten- 
examples of this condition were found in very old 
dogs. The chromophores of the skin, according to 
Metchnikoff, may be considered as chromophages. 
Whether or not they are of epithelial origin, as he 
claims, they are said to exist normally in the hairs 
in a latent or inactive condition. As old age comes 
on, or as a result of other obscure causes, their 
attitude becomes an active one, and they proceed 
to take up and digest the normal pigments of the 
hairs. Hence, white hairs are the result of an 
autoparasitism by certain mononuclear phago- 
cytes. In muscular atrophy it is held that the 
sarcoplasm takes up the striated tissue after the 
manner of phagocytes. 

We come into closer touch with our general sub- Resorption 
ject of immunity when we consider the resorptive ceils. 
function of the phagocytes for cells which are for- 
eign to the host, for example, toward erythrocytes 
which are injected for the purpose of producing a 



1XFECTI0X AXD 1MMUX1TY. 






Formation 
of Cytotoxins. 



hemolytic serum. Following such an injection into 
the peritoneal cavity there occurs a great accession 
of macrophages which ingest the erythrocytes, dis- 
solve the hemoglobin and eventually digest the 
stroma. The same phagocytes are involved in the 
resorption of any other foreign cells of animal ori- 
gin which may be injected. In view of the intracel- 
lular hemolysis by the leucocytes, one may suspect 
that the latter contain a hemolytic ferment; one 
which, perhaps, is analogous to the hemolysin 
(hemolytic amboceptors and complement) of 
serums. On this point there has been sharp dis- 
cussion. Metchnikoff cites observations to show 
that a ferment of this nature may be extracted 
from the lymphoid organs, that it contains a heat- 
susceptible constituent, and that when fresh it 
may be used to reactivate a heated hemolytic 
serum. This would indicate that the leucocytes 
contain cytase (complement), but it is not clear 
that they would also contain the fixators (ambo- 
ceptors). Nevertheless, the demonstration of an 
intraleucoc}i;ic hemolysin and a knowledge of the 
phagocytic power of the leucocytes for erythro- 
cytes form the basis for MetchnikofPs belief that 
serum-hemolysin is nothing more than intraleuco- 
cytic hemolysin, which under proper conditions 
may reach the serum or plasma. By an extension 
of this conception it is held that all cytolysins are 
produced by the macrophages. 

Korschun and Morgenroth, on the other hand, 
obtained from lymphoid and various other organs, 
sran Extracts. nc ^ a thermolabile hemolysin, but one which with- 
stands prolonged boiling — a coctostabile hemolysin 
which is soluble in alcohol, shows no amboceptor- 



Therniosta- 
bile Hemoly- 
sin from Or- 



CYTASE. 311 

complement composition, and is incapable of yield- 
ing antihemolysin by immunization. These re- 
sults, Metchnikoff holds, are only in apparent dis- 
cord with those obtained by himself and his pu- 
pils, and depend on the methods of extraction 
which were employed. In order to obtain the ther- 
molabile hemolysin uncontaminated with the ther- 
mostabile, the extraction must be a rapid one. If, 
on the other hand, it is prolonged, as Metchnikoff 
assumes that of Korschun and Morgenroth to have 
been, the intracellular ferments digest the remain- 
ing cell constituents, including the thermolabile 
hemolysin, and the thermostabile hemolysin is lib- 
erated or formed in the process. 

Believing that cytase, under normal conditions, 
exists only within the leucocytes, and that its pres- 
ence outside these cells is artificial, Metchnikoff 
cites experiments similar to the following in sup- 
port of his views : 

Given a guinea-pig which has been immunized cytase an 
with the blood of a goose : if fresh goose corpuscles substance. 
are injected into the peritoneal cavity, the cells are 
hemolyzed in the fluid without the occurrence of 
phagocytosis. Two explanations of the extraleu- 
cocytic presence of cytase and fixators, which is in- 
dicated by this result, are possible : first, that they 
are present normally and continuously in the plas- 
ma of the immunized animal, or, second, that they 
become liberated at the time the corpuscles are in- 
jected. According to Metchnikoff, the latter conten- 
tion prevails rather than the former. He recognizes 
a phenomenon which bears the name of phagolysis, piiagoiysis. 
i. e., solution, partial or complete, of phagocytes. 
Almost any foreign substance or fluid which one 






312 INFECTION AND IMMUNITY. 

may choose to put in contact with leucocytes so 
stimulates or injures them that they discharge cer- 
tain of their constituents. If the fixators and 
liberation cvtase are anions the constituents which are dis- 

of Cytase by ; ° . . 

piiagroiysis. charged at the time the injection is made, the 
extracellular hemolysis encountered in the experi- 
ment described above might depend on the libera- 
tion of these substances rather than on their nat- 
ural occurrence in the plasma. If this be true, 
and if one could in some way fortify the leucocytes 
against phagolysis, the plasma would remain free 
from hemolytic power. Metchnikoff accomplishes 
such fortification, i. e., prevents phagolysis, by a 
simple procedure, which demands nothing more 
than the peritoneal injection of a small quantity 
of bouillon or salt solution twenty-four hours in 
advance of the experiment. Possibly by this 
means the leucocytes have been habituated to the 
presence of a foreign fluid, or the new leucocytes 
which accumulate possess greater resistance. What- 
ever the explanation, the erythrocytes which are 
injected at this critical time are said not to un- 
dergo extracellular hemolysis, but instead are en- 
globed and dissolved by the macrophages. These 
results and others of a similar nature are the basis 
for the belief that cytase normally is intracellular, 
and that it becomes extracellular only when the 
leucocytes are subjected to injurious influences. 
The fact that the serum of defibrinated or coagu- 
lated blood contains cytase is not in discord with 
such an opinion, for in this instance also the leu- 
cocytes may be injured to such a degree that cer- 
tain of their constituents are discharged. We are 



PHAGOCYTOSIS IX IMMUNITY. 



313 



Fixators 
Produced l»y 

Leucocytes. 



Phagocytosis 
in Immunity. 



well aware that fibrin ferment is liberated under 
these circumstances. 

It was equally desirable, if possible, to determine 
the relation of fixators to the leucocytes. The sit- 
uation is, however, very complex, and, although 
Metchnikoff regards the fixators as secretion or ex- 
cretion products of phagocytic cells, the question 
is, perhaps, not definitely settled. When phagoly- 
sis is prevented in the manner described, the in- 
jected erythrocytes may well absorb fixators from 
the plasma and still undergo no hemolysis until en- 
globed by the phagocytes. It is considered that 
fixators in contrast to cytase may exist in the cir- 
culating plasma. 

Phagocytosis as a feature of local resistance 
against microbic invasion was considered in rela- 
tion to inflammation. We come now to speak of 
the relationship of the leucocytes to general 
states of immunity, having reference to the condi- 
tions which have been designated as natural and 
acquired antibacterial immunit} 7 ', and natural and 
acquired antitoxic immunity. 

The first expressions of Metchnikoff concerning 
the antimicrobic activity of phagocytes, the power 
of freeing the organism from "invaders of every 
sort," were made altogether from an a priori stand- 
point in an address delivered in 1883, "Ueber die 
Heilkrafte des Organismus." He justified his po- 
sition on general grounds, having in mind the 
"more general phenomena of phagocytosis and the 
resorption of corpuscular elements," as he had 
observed them in various zoological studies. 

Shortly there came to him the opportunity of Natural im 
studying an infectious disease among the Daphnia Bacteria. 



314 INFECTION AND IMMUNITY. 

(water-flea), a small transparent crustacean. The 
disease was caused by a blastonvyces which forms 
a long needle-shaped spore. After being swal- 
lowed by the animal the spores penetrate the in- 
testinal wall into the body cavity where they are 
surrounded, englobed and digested by the white 
blood corpuscles. If this occurred with sufficient 
vigor all the spores were disposed of and the ani- 
mal recovered. Sometimes, however, the spores 
germinated even after they had become intracellu- 
lar, and when the parasitic cells reached maturity 
they apparently had the power of killing the leu- 
cocytes through the agency of a secretion peculiar 
to themselves. In the event that the latter proc- 
ess was sufficiently extensive the tissues were soon 
overrun with parasites and death resulted from a 
septicemic condition. The observations were made 
in the living transparent animal. 
Natural Although the example cited seemed convincing, 
it was, of course, necessary that observations 
should extend over many infectious processes be- 
fore phagocytosis as the cause of natural immunity 
could be accepted as a general fact. This has been 
done on rather broad lines by Metchnikoff and his 
pupils, and the results have served to convince 
them that the phagocytes are responsible for nat- 
ural immunity in all instances, and that the de- 
gree of natural immunity in a given case depends 
on the degree of phagocytosis which is manifested 
against the organism. As stated previously, the 
microphage, with its microcytase, is held responsi- 
ble for antibacterial immunity in most instances, 
although the macrophage is concerned in certain 
chronic infections. 



Immunity. 



PHAGOCYTOSIS AXD VIRULENCE. 



31-3 



If an animal is susceptible to a virulent culture 
of anthrax, but resistant to a weak culture, the 
phagocytic power is found to be greater for the 
weaker organism. The highly virulent culture 
creates a condition of negative chemotaxis, with 
the consequence that leucocytes are not attracted 
and microbic proliferation proceeds rapidly. 
Without going into details, studies of the follow- 
ing and perhaps other micro-organisms have 
strengthened Metchnikoff in his views : staphylo- 
cocci, streptococcus, pneumococcus, gonococcus, 
vibrio of cholera in infections of the guinea-pig, 
the vibrio of goose septicemia in relation to the 
guinea-pig, which is naturally immune, the spi- 
rillum of relapsing fever, tubercle bacillus, yeast 
cells and other fungi, and certain animal para- 
sites (Trypanosoma lewisii). 

Most important are certain conditions which 
create a condition of negative chemotaxis, or other- 
wise engage the phagocytes so that they refuse to 
take up the essential organism. Vaillard says 
that all animals are immune to pure cultures of 
the tetanus bacillus or its spores, provided the lat- 
ter have been washed entirely free of toxin. The 
absence of toxin permits of positive chemotaxis 
and phagocytosis, whereas toxin when present 
causes negative chemotaxis, and the bacilli pro- 
ceed to further toxin formation. The same is held 
to be true in infections by some other organisms. 

It seems to be definitely established that con- 
taminating organisms (pyogenic cocci, Bacillus 
prodigiosus) may greatly increase the virulence of 
the bacillus of symptomatic anthrax, Bacillus 
Welchii. and the tetanus bacillus — anaerobic or- 



Relation of 
Phagocytosis 
to Virulence 
of Bacteria. 



Toxins as 
Cause of 
Negative 
Cheniosis. 



Accidental 
Engagement 
of Phago- 
cytes. 






31G INFECTION AND IMMUNITY. 

ganisms. On the one hand, the secondary bac- 
teria may produce more favorable conditions for 
the growth of the anaerobes by consuming local 
oxygen, or, as MetclmikofT believes, they may so 
engage the phagocytes that the latter have no dis- 
position to take up the essential organism. This 
condition may be an important one in other mixed 
infections, as when the streptococcus complicates 
diphtheria and scarlet fever. 
Acquired im- If the phagocytic power is an index of the de- 
"Bacteria! S ree °^ natural antibacterial immunity, is the same 
correspondence to be recognized when the immun- 
ity is acquired? To answer this question satisfac- 
torily it is necessary to bring phagocytosis in rela- 
tion to two different types of antibacterial immun- 
ity which it is possible to recognize. Cholera is an 
example of that type of antibacterial immunity in 
which the bactericidal power of the serum under- 
goes a great increase. It is stated that anthrax 
represents another type in which the immunity is 
not dependent on the bactericidal power of the 
serum. Probably the same may be said of acquired 
immunity to the streptococcus, staphylococcus and 
the pneumococcus, yet it is perhaps not definitely 
established that the immunity in these instances 
is antibacterial rather than antitoxic. For the 
present we may, however, with Metchnikoff, con- 
sider that the immunity is antibacterial and that 
it is a cellular or phagocytic immunhty. 
Anthrax. Rabbits which have been immunized against 
anthrax respond to subcutaneous or intraperitoneal 
injection of a virulent culture by concentrating so 
vast a number of microphages at the site of inocu- 
lation that the fluid becomes purulent in appear- 



RELATION OF SERUM TO PHAGOCYTOSIS. 317 

ance. Examination shows an enormous degree of 
phagocytosis. When, on the other hand, non-im- 
mune rabbits are submitted to similar inocula- 
tions, the fluid which accumulates locally is of a 
clear serous character, contains few leucocytes, and 
no phagocytosis is observable ; the animals die of a 
rapidly developing septicemia. From the results 
one may well suspect that the immunity is related 
to and perhaps coextensive with the acquired pha- 
gocytic power. 

But is the serum of no influence? It has often Phagocytes 

Take Ip 

been held that phagocytes take up bacteria onlv virulent 

l Bacteria. 

after the latter have been injured or killed by the 
serum or plasma. Metchnikoff answers this objec- 
tion experimentally by inoculating an immune rab- 
bit with anthrax, withdrawing some of the exu- 
date at a time when phagocytosis is complete, and 
injecting it into a non-immune rabbit. The sec- 
ond animal dies. Since none but phagocytized 
bacilli were injected into the non-immune rabbit 
( ! ) , and since the latter succumbs to anthrax, it 
seems not only unnecessary, but unjustifiable, to 
assume that the bacteria must be attenuated by 
the serum before they can be taken up by the leu- 
cocytes. May the serum, nevertheless, have some The influence 
obscure action which may not be included under 
such terms as bactericidal and attenuating? It 
seems fairly well established that anti-anthrax 
serum, at least from certain animals, may exert a 
protective influence when injected into other ani- 
mals in conjunction with or in advance of the cul- 
ture; } r et Metchnikoff discredits the importance of 
such protection and says that "those properties of 
the body fluids, as the bactericidal, preventive and 



318 INFECTION AND IMMUNITY. 

agglutinating, fall away into the background in 
such examples of immunity/ 5 It is the tendency 
of the school of Metchnikoff to refer the protective 
power of a serum to its faculty of stimulating the 
phagoc}^tes rather than to its effect on the micro- 
organisms. We shall see, however, in speaking of 
opsonins (p. 324) that even in relation to anthrax 
the serum may possess a distinct property which 
facilitates phagocytosis, not by stimulating the 
phagocytes but by some action on the bacteria. 

cholera ami Concerning those diseases in which immunity 
infections, is characterized by a great increase of the bac- 
tericidal amboceptors or fixators, Metchnikoff does 
not disregard the existence or importance of the 
immune bodies, but rather seeks to show that they 
are a product of phagocytic activity. The con- 
ditions are held to be similar to those already 
mentioned in connection with intra vitam hemoly- 
sis. That is to say, microcytase exists only in the 
leucocytes of the immune animal under normal 
conditions; it escapes into the plasma, or into the 
serum during coagulation, only as a consequence 
of the phago lysis already mentioned. The phe- 
nomenon of Pfeiffer occurs only because the in- 
jected culture injures the leucocytes, resulting in 
the liberation of microcytase, which in conjunction 
with the fixators causes the solution of the vibrio. 
When phagolysis is prevented by a preceding in- 
jection of bouillon, phagocytosis and intracellu]ar 
solution of the organisms entirely supplant extra- 
cellular solution. 
intravascular If an immune animal receives an intravascular 

phagocytosis injection of the vibrio of cholera and is sacrificed 
phag-oiysis. shortly, the relation of the organisms to the leu- 



ORIGIN OF CYTASE. 319 

oocytes may be studied in stained microscopic sec- 
tions of the organs (lungs). Leucocytes which 
have undergone phagolysis are seen to be clumped 
in the pulmonary vessels and in their immediate 
vicinity one finds many micro-organisms which 
have been changed into the characteristic granules 
by the action of the cytase which has escaped from 
adjacent leucocytes. Coincident with the phe- 
nomenon of phagolysis, the leucocytes lose their 
phagocytic power; hence, no bacteria are found 
within the leucocytes. On the other hand, all 
those vibrios which are remote from the leuco- 
cytes have a perfectly normal appearance. Phago- 
lysis in the blood stream may be prevented, just as 
' in the peritoneal cavity, by a preceding injection 
of bouillon into the vessels. In this instance when 
the culture is injected no extracellular solution or 
transformation of the organisms into granules 
takes place, but as in the peritoneal cavity, fheir 
destruction is accomplished entirely within the 
microphages. Metchnikoff holds to the correct- 
ness of these observations and interpretations, al- 
though contradictory results were obtained by 
PfeifTer and his pupils. As further evidence that 
cytase does not exist normally in the plasma Metch- Miciocytase 
nikoff cites the condition which is found in the ieiiuiar." 
anterior chamber of the eye in immune animals. 
The vibrios continue unaffected in the aqueous 
humor until such a time as leucocytes wander in, 
when they are destroyed by phagocytosis. Hence, 
cytase does not exist in the aqueous humor, and 
if not in the aqueous humor it is surely 'absent 
from the plasma; for if present in the plasma it 
would reach the anterior chamber .by a process of 



320 IXFECTIOX AND IMMUNITY. 

diffusion. Similar conditions prevail in edematous 
fluids. In another instance a portion of a vein, 
filled with blood, was resected and centrifugated 
without the formation of a clot (absence of pha- 
golysis) ; the plasma contained no cytase. Also 
Gengou collected and centrifugated blood in tubes 
which were coated with paraffin, and thus avoided 
clotting; here also cytase was absent from the 
plasma. 
increase of It would seem, then, that two important anti- 
of^pliasocytic bacterial factors characterize immunity to cholera 
power. an( ^ s i m ii ar infections : the development of specific 
fixators, and a greatly increased phagocytic power 
on the part of the leucocytes. Metchnikoff leans 
to the view that bacteria, having absorbed fixators, 
are more readily phagocytized, but no clear idea is 
given as to the change which the fixators produce. 
However, he would not refer the increased phago- 
cytic power entirely to the influence of the fixa- 
tors. He believes that the leucocytes of the im- 
mune animal have per se a higher phagocytic 
power than that of the normal animal. In anthrax, 
for example, the phagocytic power is height- 
ened in spite of the fact that there is no increase 
in specific fixators. This view, however, is op- 
posed b}' Denys and Leclef, who found that the 
leucocytes of the immune animal, when trans- 
ferred to normal serum, had no greater phago- 
cytic power than normal leucocytes. 
Fixators Metchnikoff believes that fixators, like cytase, 
3Hcropimg;e! are produced by the microphage. That the lymph- 
oid organs may form certain fixators seems prob- 
able from the observations of Pfeiffer and Marx 
in regard to cholera and Wassermann and Takaki 



LEUCOCYTIC PRODUCTION OF ANTITOXIN. 321 

in typhoid. During the process of immunization 
and at a time when amboceptors were absent from 
the serum they could be demonstrated in the blood- 
forming organs (spleen, lymph glands, bone-mar- 
row) . Metchnikoff suggests that they may be pro- 
duced in these organs by the microphages which 
have wandered in after having englobed the micro- 
organisms. In contrast to C}i:ase the fixators read- 
ily abandon the leucocytes which produced them 
and become a constituent of the plasma. 

The leucocytes have also been brought in rela- Natural 

. . -lip • Immunity to 

tionship to antitoxic immunity and the formation Toxins. 
of antitoxins. In experimental tetanus exudates 
which are rich in leucocytes contain more toxin" 
than does a similar quantity of blood. That is to 
say, the leucocytes have the power of absorbing . 
toxins, and it is held that the natural immunity 
of the animal depends on the degree to which this 
power is present. The immunity . of the chicken 
to tetanus depends not on non-susceptible nerve 
cells nor on the presence of natural antitoxin, but 
on the absorbing power of the leucocytes for the 
toxin. Not only do leucocytes absorb toxins, but 
it is held that they also are the producers of anti- 
toxins. As compared with the side-chain theory, 
it is a peculiarity of the view of Metchnikoff that 
antitoxin does not represent a constituent of the 
tissue cells, but rather the toxin itself, which has 
been altered by leucocytic activity in a manner as 
yet obscure. 

In passive antitoxic immunity the idea of a passive Anti- 
chemical union between toxin and antitoxin does n *ity? 
not meet with general acceptance among the up- 
holders of the phagocytic theory. It is sometimes 



322 INFECTION AND IMMUNITY. 

said that antitoxins are efficacious from the fact 
that they stimulate phagocytosis (absorption) of 
the toxin, the latter then suffering disintegration 
in the leucocytes. 

The following statements summarize the phago- 
cytic theory of immunity as conceived by Metch- 
nikoff : 

1. Natural immunity to bacteria depends on 
and is coextensive with phagocytosis and subse- 
quent digestion of the microbes. Intraleucocytic 
destruction of the micro-organisms is accomplished 
by the cytase, possibly aided by intraleucocytic fix- 
ators. Normal serum is devoid of both fixators 
and cytase. 

2. Acquired immunity to bacteria depends on 
the establishment of a heightened phagocytic power 
as the result of immunization or infection. In 
diseases like anthrax, in which fixators are not in- 
creased, this new power is an acquired property 
of the leucocytes and is independent of any in- 
fluence on the part of the serum. In diseases like 
cholera, the new fixators which are formed may 
render the micro-organisms more susceptible to 
phagocytosis, but this is probably secondary to 
increased function on the part of the phagocytes. 
Both cytase and fixator are produced by the pha- 
gocytic cells. In acquired active immunity to 
bacteria the fixators may be free in the serum 
and plasma, but the cytase is intracellular. In all 
cases cytase becomes extracellular only as the re- 
sult of phagolysis. 

3. In passive immunity to bacteria, as when an 
antibacterial serum is injected for the sake of 
prophylaxis or cure, the serum is efficacious chiefly 



SUMMARY. 323 

because it stimulates the leucocytes to increased 
phagocytosis. 

4. Natural immunity to toxins depends on the 
power of the leucocytes, and perhaps the genera- 
tive organs, to absorb the toxin. 

5. Active immunity to toxins is established 
through the activity of the leucocytes, by which 
the toxin is probably so changed as to constitute 
antitoxin. 

6. In passive antitoxic immunity the antitoxin 
presumably acts by stimulating the phagocytes to 
an increased absorption of the toxin. 









CHAPTER XX. 



Although the importance of the influence of 
the serum in phagocytic processes was recognized 
by Denys and Leclef, it remained for Wright and 
Douglas to demonstrate that substances exist in 
the serum which are capable of rendering bacteria 
susceptible to phagocytosis. The name opsonin 
which they applied to this substance has come 
into general use. 

The proof of the action of opsonin on bacteria 
was based on the following facts: 1. When the 
fresh defibrinated blood of some animal is mixed 
with the culture of a suitable micro-organism 
(staphylococcus, streptococcus, anthrax bacillus, 
■etc.) and placed in the thermostat for 20 or 30 
minutes, stained preparations of the mixture show 
that the polymorphonuclear leucocytes contain a 
large number of the microbes. 2. If, however, all 
the serum is washed from the blood before adding 
the micro-organisms, practically no bacteria are 
ingested. This shows the importance of the serum, 
but does not differentiate between some effect on 
the leucocytes, on the one hand, or the bacteria, 
on the other. 3. In order to decide this point one 
may subject the suspension of bacteria to the 
action of fresh cell-free serum, and after a contact 
of about 30 minutes remove all the serum by cen- 
trifugation, and mix the "sensitized" culture with 
serum-free blood; phagocytosis occurs almost to 



TECHXIC. 



325 



the same degree as when the fresh defibrinated 
blood, containing serum, is used. These results 
seem to show definitely that phagocytosis depends 
on the power of the opsonins to affect the bacteria 
in some peculiar manner. 

Later experiments showed that the opsonic 
power of the blood varied in the course of disease 
just as is found in the case of other immune sub- 
stances. The relation of such an abnormal opsonic 
power to that of normal serum was designated as 
the opsonic index. 

The Wright technic deals with three factors as 
will be apparent from the above : leucocytes, bac- 
teria and serum. 

Leucocytes. — The leucocytes are obtained in dif- 
ferent ways according to the kind employed. Human 
leucocytes are obtained by puncturing the lobe of 
the ear or tip of the finger with a small lancet 
and catching the blood in a 1 to 1.5 per cent, 
solution of sodium citrate in 0.85 per cent, sodium 
chlorid solution. The amount of blood necessary 
is usually small, about 1 c.c. and 10 c.c. of citrate 
solution is required to keep the blood from clot- 
ting. By centrifugalizing, the corpuscles are 
separated from the citrate solution and the cor- 
puscles washed by pipetting of the supernatant 
fluid and replacing it with physiologic salt solu- 
tion. Two such washings are made and then the 
pearly-colored blood cream containing the leuco- 
cytes is removed from the surface of the red cells 
for use. 

Serum. — This is obtained as for agglutination 
or other tests. 



Opsonic 
Index. 



326 INFECTION AND IMMUNITY. 

Bacteria, — The bacteria are obtained by growing 
on the surface of an agar slant for from 12 to 2A 
hours; they are then removed into salt solution 
either by means of a loop or by adding the salt 
solution directly to the agar slant. The concen- 
tration should be such that a smear on a slide 
shows plenty of bacteria to the field of the micro- 
scope while at the same time the individual organ- 
isms are well separated from one another. Fre- 
quently to obtain such a mixture it is necessary 
to shake the emulsion thoroughly to insure divi- 
sion of clumps. 

Having the above constituents they are mixed 
together in the following way : 

A capillary tube is made by drawing out a glass 
tube of about 4 mm. caliber and a length of about 
16 cm. A small volume of serum is allowed to 
run into the tube by capillary attraction and the 
length of the volume marked on the outside of 
the tube. A small air bubble about 1 mm. in 
length is then drawn into the tube and then a vol- 
ume of bacterial suspension equal to the volume 
of serum. Again a small bubble of air is drawn 
into the tube and lastly a volume of leucocyte mix- 
ture equal to those of serum and bacteria. 

The three constituents are then mixed together 
by drawing the three up into the large part of 
the tube and mixing together there by drawing 
back and forth or they may be mixed on a glass 
slide and then drawn back into the capillary tube. 
The mixture is then incubated the desired length 
of time (usually about 15 minutes) and smeared 
on a slide as in making an ordinary blood smear. 



TECHNIC. 327 

The slide is then stained with an appropriate 
stain (for most bacteria one of the eosinates of 
methylene blue) and examined with the immer- 
sion lens of a microscope. 

The number of bacteria in successive leucocytes 
is counted and an average made. Various figures 
are given as the necessary number of leucocytes 
which should be counted to give accurate results. 
The number, however, should be governed by the 
uniformity of the numbers of bacteria in succes- 
sive leucocytes. If, for instance, the average 
number of bacteria in three successive counts of 
ten leucocytes is nearly the same, it is more ac- 
curate to take such an average than if more leuco- 
C3^tes are counted with no uniformity of numbers. 

The ratio of the average number of bacteria to 
the leucocyte taken up in the presence of a given 
serum to the average number taken up in the 
presence of a serum taken as normal is the opsonic 
index. 

By the immunization of animals by various immune 
bacteria and other cells a serum of high opsonic 
power may be produced. The opsonic action of 
such serums, in contrast to that of normal serum, 
is not destroyed by heating to 56° C. and differs 
from normal opsonin in other respects which will 
be discussed later. In immunizing animals with 
typhoid bacilli, it was noticed that the estimation 
of the concentration of opsonin in the typhoid im- 
mune serum by the Wright method of comparison 
did not show results that would be expected. That 
is, a highly immune animal would show little 
difference from one with low immunity. Klien, 
therefore, estimated the opsonic power by determ- 



Opsonins. 



Opsonins. 



328 INFECTION AND IMMUNITY. 

ining the dilution point at which the number of 
bacteria taken up by the leucocytes equals the 
number taken up without the presence of serum. 
This dilution point is sometimes called the point 
of opsonic extinction. The phagocytosis taking 
place without the influence of serum is known as 
spontaneous phagocytosis. 
specificity of There has been considerable conflict of opinion 
as to whether there are specific opsonins in normal 
serum for different varieties of cells or one opsonic 
substance capable of acting on a variety of cells. 
Hektoen concludes from his own studies and those 
of others, consisting of specific absorption experi- 
ments and observations on the specific fall in 
opsonic power following injection of specific anti- 
gen, and from other experiments, that normal 
serum contains specific opsonins which are capable 
of specific absorption and which are the same 
substances which are increased to form the im- 
mune opsonin. 

The immune opsonins are easily demonstrated 
by absorption experiments to be highly, specific. 

Hektoen and Euediger have shown that normal 
opsonins are almost completely destroyed or inacti- 
vated by heat and are therefore thermoiabile. The 
inactive opsonin (opsonoid) by saturating the 
receptors of bacteria with the haptophore group 
prevents further sensitization with fresh serum. 

These investigators also show that opsonin may 
be bound or neutralized similarly to complement 
by solutions of various salts. 

The nature of immune opsonins has been the 
subject of much discussion. As was stated before, 
immune opsonins resist a temperature of from 56 



NATURE OF OPSONIN. 329 

to 60° C. Dean, Cowie and Chapin, and others 
have shown, however, that the opsonic power of 
heated serum may be increased by the addition of 
normal serum similar to that reactivation taking 
place on adding complement to amboceptor. 
Browning has pointed out that this apparent sim- 
ilarity of the action of normal serum on heated 
opsonin may be due to summation of effects. He 
has shown that by separating immune body in 
opsonic serum at 0° C. by saturation with bacteria 
and then adding complement there is a true activ- 
ation, and that no such action occurred in treating 
the bacteria with complement, washing and then 
adding heated opsonic serum. He concludes tllat 
, immune body and complement may be concerned 
in opsonic action, but leaves open the question of 
whether the immune body is the thermostabile 
opsonin or not. 

Hektoen concludes from the following facts that opsonins as 
opsonins are distinct from other antibodies. Antibodies. 

1. Heat may almost completely destroy the 
opsonic power of serum leaving the lytic ambo- 
ceptors intact. 

2. Serum, normal as well as immune, may con- 
tain opsonin for a given organism but not, at least 
so far as is known, the proper lytic amboceptor for 
that organism. 

3. A serum may contain opsonin for an organ- 
ism, but no agglutinin and the opsonin may persist 
after destruction of bacteriolytic complement by 
heat. 

4. In immunization lytic and opsonic powers do 
not run parallel. 



330 INFECTION AXD IMMUNITY. 

Relation to If an animal is injected with a proper dose of 
p^oSesseJ bacteria or alien red cells, there results as a rule 
in the first day or so a fall in the opsonic content 
of the blood along with other antibodies. This 
period is known as the "negative phase," and is 
followed by a steady rise which reaches its height 
from the eighth to the twelfth day and gradually 
falls to normal. The negative phase as pointed 
out by Hektoen is specific and it has not been 
determined whether it is due to a specific absorp- 
tion or to an effect on the antibody producing 
cells. 

"In several acute infectious diseases the course 
of the formation of new opsonin for the infecting 
agent, in the typical attack, terminating promptly 
in recovery without complications, shows a marked 
general resemblance to the opsonin and antibody 
curve after a single antigen injection in the 
normal animal; it also bears definite and constant 
relations to the clinical phenomena. During the 
early stages when the symptoms are pronounced 
there is a negative phase and then as the symptoms 
begin to subside the opsonin curve rises above 
normal, reaching the highest point several days 
after the onset, followed by a gradual subsidence. 
This is true of the pneumococcus opsonin in pneu- 
monia, of the opsonin for the diphtheria bacillus 
in diphtheria, of the streptococcus opsonin in 
erysipelas, and also of the opsonin for the dip- 
lococcus of mumps in that disease. The curve is 
typical also for the streptococcus in scarlet fever, 
indicating clearly that this organism unquestion- 
ably plays a definite role in scarlet fever, whatever 
its actual causative relation to the disease may be. 



IMPORTANCE OF OPSONINS. 331 

In pneumonia the greatest rise in the leucocytosis 
appears to precede somewhat the highest rise of 
the opsonin. In all these diseases the typical 
wave-like opsonin curve is modified by the devel- 
opment of complications of various kinds and at 
the onset of which it commonly undergoes a dis- 
tinct depression. In rapidly fatal cases, for in- 
stance of pneumonia, the opsonic curve or index 
may not return from the primary depression, but 
sink lower and lower. In prolonged infections, 
general as well as local, there occur irregular 
fluctuations and in chronic, more or less stationary 
cases, the opsonic index is often subnormal. At 
this time further details cannot be given. My 
chief point is to make clear the close association 
between recovery and the wave-like rise of the 
opsonin, and, as a result of the immunization in 
all likelihood also of other antibodies, in the 
typical attack of acute so-called self-limited in- 
fections. In some of the diseases the opsonin is 
the only antibody that we can measure readily 
with our present means. As I have stated, an 
intraphagocytic destruction of pneumococci and 
streptococci takes place in the presence of fresh 
leucocytes and opsonic serum, whereas either alone 
constitutes a good medium for these bacteria. 
Taking these facts into account it seems to me 
that the wave-like course of the opsonin in pneu- 
monia and in acute streptococcus infections is a 
strong point on the side of the signal importance 
of phagocytosis in their healing, whatever other 
measure, of which at present we know less or 
nothing, may be in operation also." 1 

1. Hektoen : Opsonins and Other Antibodies, Science, 1909. 



332 



IXFECTIOX AXD IMMUX1TY. 



Interaction 
of Action of 

Leucocytes 
and Opson- 
ins. 



Hypothesis 
of Welch. 



As pointed out by Glynn and Cox, the work of 
Wright and his followers has resulted in an undue 
neglect of the importance of the variation in the 
power of leucocytosis in the leucocytes themselves 
as a factor in phagocytosis. They emphasize the 
fact that while the determination of opsonic power 
may be an indication of the degree of immunity, 
it does not represent the phagocytic power of the 
blood as a whole. In order to ascertain the 
valuation of the different components separately 
and as a whole they suggest the comparison of the 
leucocytes of the blood in question- with those of 
normal blood and call the ratio of the first to the 
second the cytophagic index. Secondly, they com- 
pare the action of the leucocytes and the serum 
of the blood in question with the action of normal 
leucocytes and serum. The ratio of the first to 
the second is called the opsonocytophagic index. 

What has come to be known as the hypothesis 
of Welch is of such practical and theoretical im- 
portance that reference to it should not be passed 
over. It may be put in the form of the following 
question : If bacterial toxins and the constituents 
of bacterial cells so act on the tissue cells that the 
latter produce bodies (antibodies) which are in- 
imical to the bacteria, why may not the body fluids 
in turn so act on the bacteria that the latter pro- 
duce bodies (antibodies) which are inimical to the 
tissue cells? "Looked at from the point of view 
of the bacterium, as well as from that of the 
animal host, according to the hypothesis advanced, 
the struggle between the bacteria and the body 
cells in infections may be conceived as an im- 
munizing contest in which each participant is 



HYPOTHESIS OF WELCH. 333 

stimulated by its opponent to the production of 
cytotoxics hostile to the other, and thereby en- 
deavors to make itself immune against its an- 
tagonist." (Welch.) 

A more reasonable hypothesis could hardly be 
advanced, and no small number of facts known 
at the present time are in harmony with it. 
Walker had already performed work of a funda- 
mental character, which showed that the typhoid 
bacillus, when grown in the presence of its anti- 
serum, acquires greater virulence for animals. 
Furthermore, a greater dose of protective serum 
was required to save guinea-pigs from infection, 
with the immunized culture than from the same 
strain which had not been immunized. The fact 
has been known for a long time that the typhoid 
bacillus resists agglutination when freshly cul- 
tivated from a patient having the disease, whereas 
it becomes easily agglutinable after a period of 
artificial cultivation. It may well be assumed that 
the bacillus, when playing the part of an infecting 
organism, gradually was immunized against the 
agglutinating properties of the patienfs serum; 
and, on the other hand, that it lost this resistance 
after it had been removed from the stimulating 
influence of the infected body. This immuniza- 
tion with agglutinins may be carried on in the 
test glass, and bacteria which have been so treated 
acquire the power to absorb a greater quantity of 
agglutinin from the homologous serum (Bail). 

Another pertinent observation was that by 
Wechsberg, who found that a strain of the diph- 
theria bacillus when grown in a medium contain- 
ing diphtheria antitoxin could be made to pro- 



334 INFECTION AND IMMUNITY. 

duce diphtheria toxin more abundantly. We may 
assume that the antitoxin combined with the cor- 
responding receptors situated in the bacilli (diph- 
theria toxin), and that the bacilli were, as a result, 
stimulated to produce a greater number of such 
receptors (toxin). 

Consistent as these observations are with the 
hypothesis under discussion, Welch meant a great 
deal more than the immunization of the bacteria 
against the defensive powers of the animal body. 
Not only may a bacterium during infection become 
more resistant to the bactericidal action of the 
body by producing antibodies for those bactericidal 
agencies, or by its ability to absorb and dispose of 
a greater quantity of bacteriolysin; and not only 
may a bacterium be able to respond to the presence 
of natural antitoxins in the body by the 'produc- 
tion of more toxin; but, in addition, certain con- 
stituents of our bod}^ fluids may, by combining 
with suitable bacterial receptors, stimulate the 
bacterium to the production of a whole shower of 
cytotoxins, which attack the leukocytes, erythro- 
cytes, nerve cells, liver, kidney, etc. The nature 
of the animal substances which may combine with 
the bacterial receptors and thus cause the forma- 
tion of the bacteriogenic cytotoxins is left an open 
question, and is not of essential importance for 
the theory; it is not at all necessary that they be 
toxic for the bacterium, and they may even be 
taken up as food substances. Likewise the possible 
nature of the c}'totoxins produced by the bacterium 
is of secondary importance. It so happened that 
Welch assumed that they might be of the nature 
of amboceptors, which may become complemented 



HYPOTHESIS OF WELCH. 335 

by bacterial complement, by the circulating com- 
plement of the body or by enclocomplements of 
the tissue cells. One could with equal reasonable- 
ness assume that they may be complete toxins, 
receptors of the second order, with a haptophorous 
and a toxophorous structure. 

A well-known statement of Metchnikoff is to 
the effect that a particular bacterium when viru- 
lent is not so readily taken up by leucocytes as is 
an avirulent strain. This fact has been noted re- 
peatedly in recent times in the study of phagocy- 
tosis in the test tube. This may be because the 
organism, in its virulent parasitic state, secretes 
substances which repel the phagocytes, neutralize 
the opsonins, or because of the formation of actual 
leucocytic toxins. 

One of the - most widely known phenomena in 
relation to the virulence of some organisms is that 
their pathogenicity may be increased by passing 
them through suitable animals repeatedly. The 
best results are obtained when intermediate arti- 
ficial cultivation is avoided and the inoculations 
are made directly from the dead into the living 
animal. It may, with all reason, be assumed that 
by continued residence in the host the bacterium 
has been trained to produce a greater quantity of 
toxic substances which are inimical to the host, 
and that the increased virulence of the parasite 
depends on this condition. 

Although up to the present time systematic 
attempts to place the hypothesis of Welch on a 
firm experimental basis appear not to have been 
made, the observations cited, as well as others 



336 INFECTION AND IMMUNITY. 

which could be enumerated, provide cumulative 

evidence of its correctness. 

AGGRESSINS 

Aggressins. Xot entirely foreign to the subject discussed 
above is the so-called aggressin theory of Bail, the 
essential points of which may be given without 
entering into a detailed discussion. 

Bail attributes to pathogenic bacteria the prop- 
erty of "aggressiveness," through which they 
directly antagonize the protective agencies of the 
body. The micro-organisms of highest parasitic 
powers, the "true parasites," as those belonging to 
the hemorrhagic septicemia group, possess the 
greatest aggressiveness, since they are able to pro- 
liferate in the blood stream while the antibacterial 
activities of the body (phagocytosis, etc.) are held 
in abeyance. Other bacteria, which in causing 
disease tend to remain localized, and, if by any 
means they reach the blood stream, are not able 
to proliferate greatly in this place, are "half 
parasites" and have a lower degree of aggressive- 
ness; they are more susceptible to phagocytosis 
and to the action of bacteriolysins (typhoid, 
cholera, dysentery). Saprophytes have no aggres- 
sive action. 

This is very general, but Bail and his co-workers 
have attempted to put the conception on an experi- 
mental basis by demonstrating the existence of a 
substance on which the aggressiveness of bacteria 
depends; to this substance they give the name of 
"aggressin." 

Intraperitoneal inoculation of the tubercle bacil- 
lus into the guinea-pig leads to more or less 



AGGRESSINS. 337 

general tuberculosis and to the death of the animal 
in the course of a few weeks. If, during the 
course of the disease, a second injection of a large 
quantity of the bacillus is made into the peritoneal 
cavity, or if an injection of tuberculin is given, 
the animal dies very quickly. This is, of course, 
nothing more than the well-known hypersuscep- 
tibility of tuberculous animals to the products of 
the tubercle bacillus. In addition to this fact, 
however, a similar result was obtained in another 
manner. If a large quantity of bacilli is placed 
in the peritoneal cavity of a healthy guinea-pig, 
and the exudate is removed after twenty-four hours 
and freed from leucocytes and bacilli, the aggressin 
of the bacillus is said to be present in the "clear 
fluid. This is demonstrated by injecting some of 
the fluid, together with tubercle bacilli, into the 
peritoneal cavity of another healthy guinea-pig 
The rapid death of the animal is the result, 
whereas the bacilli alone cause death only after a 
long period, and the cell-free exudate alone is 
without toxicity. 

A similar condition has been found in experi- 
mental infections with a number of bacteria 
(typhoid, cholera, dysentery, plague, chicken cho- 
lera), the essential fact being the same: that, fol- 
lowing intraperitoneal or intrapleural inoculation, 
the resulting exudate, when freed from leukocytes 
and bacteria, has the power of intensifying an in- 
fection by the corresponding organism. 

There seems at present to be no definite knowl- 
edge concerning the nature of these aggressins, al- 
though Bail thinks they may resemble true toxins 
in some respects. Likewise the precise character 



338 INFECTION AND IMMUNITY. 

of their action is unknown, although Bail and his 
co-workers are strongly inclined to the view that 
they inhibit phagocytosis by some direct action of 
the leucocytes. 

It is further interesting that immunization with 
aggressins is said to give rise to the formation of 
antiaggressins, and that by the use of antiaggres- 
sive serum the action of the aggressins is neutral- 
ized, and the bacteria consequently become the 
prey of the leucocytes. The action of the anti- 
aggressive serum is said not to depend on the pres- 
ence of bacteriolysins. 

Proof of the non-identity of the aggressins of 
Bail and the toxins produced by the organism 
has not been very convincing. 

Investigating the resistance of virulent pneu- 
mococci (which vary greatly from non- virulent 
forms) to phagocytosis, Rosenow was able, by au- 
tolysis in salt solution, to extract the substance 
on which this resistance depends. He was not 
only in this way able to render them phagocytable, 
but also by treating non-virulent strains with this 
extract he was able to render them more virulent 
and resistant to phagocytosis. 

The substance which he calls virulin is insoluble 
in alcohol and ether, and is thermostable. 






CHAPTER XXI. 



THE SIDE-CHAIN THEORY OF EHRLICH AND ITS 

RELATION TO THE THEORY OF 

PHAGOCYTOSIS. 



Side-Chain 
Theory Ap- 
plied to 
Nutrition. 



In 1885, before the discovery of toxins and anti- 
toxins and before there was any knowledge as to 
the real nature of immunity, Ehrlich 1 published a 
small volume on the "Oxygen Requirements of the 
Body." Herein the belief was expressed that the 
assimilation of foods by cells is accomplished only 
after chemical union has taken place between the 
food substance and some constituent of cellular 
protoplasm. It is not the understanding that as- 
similation is at an end, however, when this union 
has occurred, for certain molecules of complex 
chemical nature and of great -size must be split up 
into simpler substances before they can enter into 
the composition of protoplasm. Therefore, the cell 
constituent which combines with the nutritious 
molecule serves only as a link to bring the food- 
stuff into relation with the digestive, oxidizing or 
fermentative activities of the cell. 

Ehrlich speaks of that portion of living proto- 
plasm which represents the cellular activities as sme^-chains. 
the "Leistungskern" of the cell, the center of cel- 
lular activity, or the central group of the proto- 
plasm, whereas those chemical groups which bind 
the food substances are called the side-chains of the 
"Leistungskem!* 

The author of the theory has made his concep- 

1. Ueber das Sauerstoffbediirfnis des Organismus. . 



"L.eistung's- 
ltern" and 



340 INFECTION AND IMMUNITY. 

tion more tangible through an analogy which was 
drawn with the so-called ring or nucleus of benzol 
and its side-chains. The molecule of benzol, C 6 H flJ 
has a definite formation in which each carbon 
atom is linked to two others in such a manner as 
to form a ring; three valences of each carbon 
atom are satisfied in this way, and the fourth is 
satisfied by atoms of hydrogen, one of which is at- 
tached to each carbon atom, thus : 



C-H 
i-H 

II 



This ring is analogous to the "Leistungskcm" of 
the cell. A great variety of chemical compounds 
exists and very many may be produced syntheti- 
cally by substituting for one or more atoms of 
hydrogen, one or more other groups of atoms which 
may be very simple or very complex. The groups 
which have been substituted are called side-chains. 
Thus benzoic acid is formed from benzol by sub- 
stituting the acid radical COOH for a particular 
H, and the COOH in this instance is a side-chain 
of the ring : 

o 

c 
I 

c 
/ * 

H-C C-H 

II I 

H-C C— H 

\ // 

C 

I 

H 



SIDE-CHAINS. 341 

Just as the side-chains of the "Leistungskerri" 
may combine with food particles, so may the side- 
chains of the benzol ring combine with other 
groups of atoms and thereby assimilate the latter, 
so to say, into the ring. To choose a simple exam- 
ple, the sodium of sodium hydroxid may unite with 
the side-chain COOH to form sodium benzoate, 
the hydrogen of the acid radical being replaced by 
the sodium, thus : 

o 

// 
c 

I ^O-Na 
C 
/ * 
H— C C-H 

H I 

H-C C-H 

\ // 

C 



Presumably it is in some such manner as sodium 
is brought into relationship with the benzol nu- 
cleus, in the example cited, that the food sub- 
stances are brought into relationship with the 
"Leistungskern\ of the cell. 

The hypothesis of Ehrlich carries with it the Haptophores. 
assumption that the side-chains of a cell possess or 
consist of definite groups of atoms capable of unit- 
ing chemically with certain other definite groups 
of atoms in the food particles ; hence both the side- 
chain and the food substance have combining 
groups — haptophores. The side-chains of the cells 
Ehrlich now calls receptors, elements which we 
have already recognized in connection with im- 
munity. Inasmuch as different foods have differ- 
ent chemical compositions, it is likely that their 
binding groups are not identical ; and if this be 



342 INFECTION AND IMMUNITY. 

true there must exist many kinds of receptors each 
of which is able to unite only with that food sub- 
stance which has a corresponding binding group of 
atoms. 

In contrast to the condition with respect to 
foods, it is held that chemical substances of known 
composition, drugs and alkaloids never become in- 
corporated as a part of the protoplasm, that is, 
they do not unite with cell receptors, although 
they may affect the vitality and function of proto- 
plasm profoundly. Their inability to 3d eld anti- 
bodies as a result of immunization is supposed to 
depend on this condition. Such substances, ac- 
cording to Ehrlich, exist in the cell in a condition 
of unstable salt formation with some constituent 
of the protoplasm, or in a state of solid solution. 

The following statement from a recent publica- 
tion by Ehrlich summarizes the nutritional aspect 
of the theory: "We must assume that all sub- 
stances which enter into the structure of proto- 
plasm are fixed chemically by the protoplasm. We 
have always distinguished between assimilable sub- 
stances which serve for nutrition and which enter 
into permanent union with the protoplasm, and 
those which are foreign to the body. ISTo one be- 
lieves that quinin and similar substances are as- 
similated, that is, enter into the composition of the 
protoplasm. On the other hand, the food sub- 
stances are bound in the cells, and this union must 
be considered as chemical. One can not extract a 
sugar residuum from cells with water, but must 
first split it off with acids in order to set it free. 
But now such a chemical union, like every syn- 
thesis, demands the presence of two binding 



SIDE-CHAIN THEORY OF IMMUNITY. 343 

groups of maximal chemical affinity, which are 
suited one to the other. The binding groups which 
reside in the cells and which bind food substances 
I designate as side-chains or receptors, while I 
have called those of the molecules of foodstuffs the 
baptophorous groups. I also assume that proto- 
plasm is endowed with a large series of such side- 
chains, which through their chemical constitution 
are able to bind the different foodstuffs and there- 
by provide the prerequisite for cellular metabol- 
ism." 

If the side-chain theorv of nutrition is to be- side-chain 

" . . Theory Ap- 

come the side-chain theory of immunity it is nee- plied to 
essary that it undergo elaboration in order that the 
formation of antibodies may be adequately ex- 
plained. If, as Ehrlich assumes, the union of 
toxin with cell receptors causes the overproduction 
of the latter as antitoxin, and if this union is an- 
alagous to that of food substances with similar re- 
ceptors, one may wonder that antibodies are not 
formed for our ordinary foods, antibodies which 
would be discharged from the cells and which 
would unite with circulating nutritious particles 
and thereby bring about a condition of starvation. 
Without entering into the intricacies of this ques- 
tion, it seems probable that normally a condition 
of physiologic equilibrium exists between the food 
substances on the one hand and the cellular activi- 
ties on the other, so that the union of food with 
protoplasm constitutes no abnormal stimulus to 
the "Leistungskem" of the cell. When, however, 
cells are diverted from their normal metabolic 
function by union with toxins and other "abnormal 
food substances," the effect on the cell is de- 



344 INFECTION AND IMMUNITY. 

scribed as a cell defect, the defect consisting of the 
functional elimination of the receptor. The "Lets- 
tungskern" as the vital or regulating center of the 
cell repairs the defect by the formation of new re- 
ceptors, and in harmony with the hypothesis of 
Weigert produces not only enough to repair the 
defect, but a great excess, with the result that 
many are thrown into the circulation. The anal- 
ogy of the "Leistungskern" with the benzol ring 
can no1 be carried to this extent, for the latter has 
no power of reproducing side-chains to take the 
place of one which has been bound by some new 
group of atoms. 
Essential It will be appropriate in this place to consider 

Tenets off -T 

Ehriich's the character of the proof which has been offered 

Theory 

in support of the three tenets which constitute the 
framework of the theory of Ehrlich. These three 
tenets may be expressed as follows: 1. Antitox- 
ins counteract toxins by entering into chemical 
union with them; a similar union takes place be- 
tween other antibodies and their homologous sub- 
stances. 2. Toxins in injuring cells combine 
chemically with a definite constituent of the proto- 
plasm, the cell receptor; other antigenous sub- 
stances 2 enter into similar union with the appro- 
priate receptors of cells. 3. The specific antibodies 
of the serum are new-formed receptors identical in 
structure with those which, as cell constituents, 
had combined with the homologous antigens. 
chemical First tenet : In the early days of studies on im- 
Antibodies munity (1890-1897), the action of a toxin and the 
sens" efficacy of an antitoxin could be determined only 

2. An antigen or an antigenous substance is one which 
is able to cause the formation of an antibody. 



UNION OF ANTIBODIES "WITH ANTIGENS. 345 

by injecting these substances into living animals, 
and the animal experiment naturally continues to 
be the means of testing the curative and prophy- 
lactic values of serums. So long, however, as such 
experiments were performed exclusively in the liv- 
ing animal the nature of the action of antitoxin 
remained to a certain extent in doubt. It re- 
mained uncertain whether antitoxin is protective 
because it actually destroys the toxin, because neu- 
tralization of a chemical nature occurs, or because 
in some manner it increases the resistance of the 
inoculated animal. In Chapter XII experiments 
were cited to show that antitoxin does not destroy 
the toxin, and this is generally admitted to-day. 
There continues to be some difference of opin- 
ion, however, in relation to the two other possibili- 
ties, i. e., as to whether antitoxin combines chemi- 
cally with toxin, or is efficacious because of its 
stimulating power on the tissues of the animal. 
Behring, the discoverer of antitoxin, was from the 
beginning an exponent of the chemical theory, even 
at a time when the conceptions of Ehrlich had not 
been fully developed. On the other hand, certain 
noted investigators, especially Eoux and Buchner, 
and later Metchnikoff, stood for the alternative 
view. 

Following closely on Behring's great discovery, Ricin and 
Ehrlich studied the hem agglutinating toxin ricin, 
from the castor-oil bean, and by immunization 
with it produced a specific antitoxin, i. e., anti- 
ricin. Eicin is toxic to erythrocytes both in the 
animal body and in the test-tube, and if it could 
be shown that antiricin protects in the test-tube 
by a direct effect on the toxin, it was highly prob- 



INFECTION AND IMMUNITY. 



Chemical Na- 
ture of the 
Neutralization 
of Toxins by 
Antitoxins. 



able that its action in the animal body would be of 
a similar nature. The results left no doubt in the 
mind of Ehrlich that antiricin unites chemically 
with ricin, and the applicability of this principle 
in animal experiments became all the more ap- 
parent when it was shown that the proportion of 
antiricin which protects in vitro also protects in 
vivo. It is held that similar proof of chemical union 
between bacterial hemolysins, the hemolysin of 
venom and the leucocidin of the staphylococcus 
with their respective antitoxins is equally valid. 
Although the animal body can not be dispensed 
with in testing the action of the antitoxins of 
diphtheria and tetanus, certain principles of chem- 
ical action are found to prevail which leave no 
doubt in regard to the chemical neutralization of 
the toxins. If neutralizing proportions of diph- 
theria toxin and antitoxin be mixed in a test-tube 
and injected immediately, the serum does not af- 
ford absolute protection; if, however, the mixture 
is allowed to stand for from fifteen to twenty min- 
utes before injection, the protection is absolute. 
This alone would point to an action of the anti- 
toxin on the toxin, for the completion of which -a 
certain amount of time is required. For the com- 
plete neutralization of tetanus toxin by its anti- 
toxin about forty minutes are necessary at ordinary 
temperatures. Then certain other chemical princi- 
ples described in Chapter XII, are found to hold 
true : That neutralization proceeds more rapidly 
at higher than at lower temperatures, more rapidly 
in concentrated than in dilute solutions, and that 
it takes place in accordance with the law of mul- 
tiple proportions. 



UNION OF ANTIBODIES WITH ANTIGENS. 347 

Granting, then, that neutralization of toxin by 
antitoxin is of a chemical nature, the first essential 
step in the chemical or side-chain theory is estab- 
lished. If antitoxin combines chemically with 
toxin, union must occur through combining groups 
which each molecule possesses. Herein lies the ex- 
perimental justification for assuming the existence 
of haptophorous groups. 

The situation is more difficult in regard to the union of a&- 
union of receptors of the second and third orders, Amboceptor 
i. e., agglutinins and amboceptors with the ho- Receptors. 
mologous receptors of bacteria and other cells.- 
One can not titrate bacteria against agglutinin or 
bactericidal amboceptors so exactly as toxin can be 
titrated against antitoxin, for, in the first place, 
it is difficult to obtain at will a desired concentra- 
tion of bacteria and to keep it without alteration, 
and, in the second place, bacterial cells contain 
many more receptors than are necessary for their 
agglutination and solution. A given mass of bac- 
teria will take up varying quantities of agglutinin, 
depending on the concentration of the latter, and 
the same principle applies to the absorption of 
bactericidal and hemolytic amboceptors. As more 
and more agglutinin is added, the total amount 
absorbed increases with each addition, although 
the ratio of absorbed to unabsorbed agglutinin 
grows less continuously. The conditions which 
govern this phenomenon are not understood. 
Perhaps no condition speaks more decisively for 
chemical union of these bodies with cell receptors 
than immunization experiments which were car- 
ried on with cells which had been treated with a 
great excess of the specific antiserum. The as- 



348 INFECTION AND IMMUNITY. 

sumption was made that if one could force all the 
receptors of erythrocytes, for example, to take up 
the specific amboceptors, such corpuscles should 
lose their power to cause the formation of a hemo- 
lytic serum when injected into a suitable animal. 
This would follow logically, for the receptors of 
the corpuscles, being already bound, would not be 
free to unite with receptors of the immunized ani- 
mal. Antibodies were not formed under these cir- 
cumstances, from which it is concluded that the 
receptors of the erythrocytes had united chemi- 
cally with the antibodies of the serum (Sachs). 
In order to completely occupy all the receptors of 
the vibrio of cholera Pfeiffer used 3,000,000 to 
-i.000,000 times the dissolving amount of the anti- 
cholera serum. Although the mere absorption of 
agglutinins and amboceptors by the homologous 
cells is cited in favor of the chemical hypothesis, 
we may bear in mind the contention of certain in- 
vestigators that this absorption is physical rather 
than chemical. 
Chemical \a- Second tenet: What evidence have we that tox- 
of 1 Toxin^ I1 an , ci i ns anc *- °ther antigenous substances enter into 
other Aiiti- chemical union with receptors in the cells of the 

gens with r 

Ceii Recep- immunized animal ? It is probable that no ob- 

tors. x 

servation speaks more strongly in favor of such 
union than a famous experiment of Wassermamr's 
in which the central nervous system of guinea- 
pigs was ground up with tetanus toxin, the mix- 
ture allowed to stand for a short time and then 
injected into mice. The mixture was found to be 
non-toxic, and further experiments showed that 
the neutralizing power resides in the solid tissue 
in the emulsion. It is claimed by Ehrlich that 






ANTIGEN AND CELL RECEPTORS. 349 

this experiment demonstrates positively that 
chemical union of tetanus toxin takes place with 
constituents of the nervous tissue. The toxin hav- 
ing been completely neutralized can not again be 
extracted from the tissue. The condition is the 
opposite in relation to some poisonous alkaloids, 
as strychnin, which it appears does not combine 
with the protoplasm firmly and may again be ex- 
tracted by simple methods. 

Von Dungern conducted very important work 
with the precipitins, which is interpreted as show- 
ing that albuminous substances other than toxins 
are taken up chemically by the cells. He injected 
considerable quantities of a foreign serum into the 
veins of rabbits and studied its disappearance from 
the blood of the injected animal. Traces of the 
foreign serum could be recognized by treating the 
rabbit serum with a specific precipitin for the for- 
mer, the precipitin having been obtained pre- 
viously by the immunization of other animals. 
The foreign serum disappeared from the circula- 
tion of the rabbit with some rapidity and since it 
could not be demonstrated in the excretions, it 
seemed necessary to assume that it had been bound 
by the cells, that is to say, by the cell receptors. 

Third tenet: Is there any direct experimental Proliferation 
proof that those constituents of cells which have 
been designated as cell receptors actually undergo 
multiplication in the cell itself as a preliminary to 
their discharge into the circulation in the form of 
antibodies? If this condition could be demon- 
strated in one instance, one might reasonably con- 
sider that it typifies a law according to which all 
antibodies are formed. Further experiments by 



350 INFECTION AND IMMUNITY. 

von Dungern with the precipitins seem to show 
that such intracellular overproduction actually 
does occur. The experiments concern the fate of 
"Majaplasma" (plasma of the spider-crab) when 
injected into the circulation of the rabbit (see 
above). If a single injection of the serum is 
given, a specific precipitin for the latter body in 
due time may be demonstrated in the serum of the 
rabbit. Eventually the precipitin disappears from 
the circulation by excretion or other means. At 
that time, when all the precipitin has disappeared, 
one may assume that the cells of the animal still 
contain an increased number of precipitin recep- 
tors, although the latter are no longer produced to 
such an extent that they are thrown into the cir- 
culation. If this condition exists the tissues of 
the animal at this time should be able to absorb a 
larger amount of the foreign serum, given in a sec- 
ond injection, and perhaps absorb it more rapidly 
than the tissues of an untreated rabbit. Using a 
specific precipitating serum in order to detect 
traces of the foreign serum which still remained in 
the blood of the injected animal, von Dungern de- 
termined that its tissues actually do absorb the 
plasma more rapidly than do the tissues of the 
untreated rabbit. The cells of the former have a 
greater absorbing power, i. e., a greater binding 
power for the plasma; therefore, an increased 
number of receptors. 

These examples are, perhaps, sufficient to illus- 
trate the principles of experimentation which have 
been followed in the attempt to obtain definite 
proof of the correctness of the essential points of 
the theory. The results are in entire accord with 



RECEPTORS. 351 

the primary assumptions and show that the theory 
continues to serve as an explanatory basis for 
newly-discovered facts, and as a foundation on 
which new researches may be instituted. 

In addition to the three main principles treated other impor- 
of above, the following points are necessarily in- cipies of 
eluded in a summary of the views of Ehrlich, many 
facts of a corroborative nature having been ascer- 
tained in independent laboratories. 

1. The recognition of different types of tissue 
receptors by which peculiarities in the action of the 
different antibodies are explained. Eeceptors of 
the first order, as antitoxins, anticomplements and 
antiamboceptors, are regarded as relatively simple 
bodies because no other constituent can be recog- 
nized than the haptophorous group by which they 
combine with their homologous substances. Ee- 
ceptors of the second order are more complicated 
in that they have something more than the mere 
binding power; usually they are able to produce 
some observable change in the substance with 
which they unite. Hence, each has a toxophorous 
or a zymotoxic group in addition to the hapto- 
phorous, and the two groups are part of the same 
molecule. Toxins, agglutinins, precipitins and 
complements are receptors of the second order. 
Receptors of the third order, i. e., the bacterio- 
lytic, hemolytic and cytotoxic amboceptors, are 
still more complex in that they are, so to say, only 
partial antibodies, the complete body consisting of 
the amboceptor-complement complex. The ambo- 
ceptor is not an active body, but serves as an in- 
termediary body to connect the active substance, 
complement, with the cell. In the C}i;olytic proc- 



352 . INFECTION AND IMMUNITY. 

ess the amboceptor through its cytophilous hapto- 
phore first unites with the cell, and as a result 
acquires an increased affinity for complement, 
with which it unites through its complemento- 
philous haptophore. Only after this double union 
is completed may complement affect the cell. 
From this it follows that complement in the cyto- 
lytic process does not combine with the cell di- 
rectly. As previously stated, Bordet and others 
oppose the idea that the absorption of these bodies 
is of a chemical nature, considering it rather to be 
a physical process. 

Ehrlich has intimated his belief that tissue am- 
boceptors play the chief role in the fixation of 
foods by the cells of the body. 

2. The chemical theory explains the specificity 
which characterizes the formation, and action of 
antibodies. Every antigen has a haptophore which 
is different from those of other antigens; conse- 
quently, it unites only with the corresponding cell 
receptor, and the latter when overproduced and 
cast into the circulation retains its specific binding 
power for the corresponding antigen. 

3. The multitude of antibodies which have been 
obtained indicate that the cells contain a vast 
number of different receptors which correspond to 
the three types now recognized; that is, there is a 
different antitoxin receptor for every kind of 
toxin, etc. 

4. Ehrlich has limited the application of the 
term toxin to those substances of animal or plant 
origin, immunization with which causes the forma- 
tion of specific antitoxins. Other characteristics 
have been given in Chapter XI. 



RECEPTORS. 353 

5. Receptors of the second order, toxins, agglu- 
tinins, precipitins and complements, undergo a 
peculiar degenerative change, spontaneously or as 
a result of exposure to injurious agents, in which 
the toxophorous or zymotoxic group disappears or 
is rendered inactive. The termination -oid is af- 
fixed to the altered bodies, as toxoid, agglutinoid, 
precipitoid and complementoid. Wechsberg has 
described a similar degeneration of one of the hap- 
tophores of amboceptors, calling the product am- 
boceptoid. Toxoids and complementoids on im- 
munization cause the formation of corresponding 
antitoxins and anticomplements, by virtue of re- 
tention of their haptophorous groups. 

6. By means of a special technic devised for 
studying the neutralization of toxin by antitoxin, 
i. e., the partial saturation method, Ehrlich found 
diphtheria toxin to be a very complex substance. 
Not all the molecules of the toxin have the same 
affinity for antitoxin, and according to the de- 
grees of their affinity have received the names of 
prototoxin, deuterotoxin and tritotoxin. Simi- 
larly, protoxoids and syntoxoids are molecules of 
toxoid having different affinities for antitoxin. 
These conditions are represented graphically by 
means of the "toxin spectrum" described pre- 
viously. 

7. Ehrlich claims that the diphtheria bacillus 
secretes two toxins, one of which causes the acute 
manifestations of diphtheritic intoxication, where- 
as the second toxin, i. e., toxon, has a prolonged 
incubation period and probably causes diphtheritic 
paralysis. Toxon has a lower affinity for diph- 
theria antitoxin than the other constituents of the 



354 INFECTION AND IMMUNITY. 

toxin solution, but is neutralized by the same anti- 
toxin. This view is strongly opposed by Arrhe- 
nius and Madsen, who, working on the basis that 
the neutralization of toxin takes place according 
to certain laws of physical chemistry, claim that 
toxon is nothing more than toxin which has disso- 
ciated from the toxin-antitoxin molecule. 

S. It is thought that the incubation period 
which characterizes the action of toxins represents 
to a large degree the time required for the action 
of the toxophorous group after the toxin has been 
bound by the cells. 

9. Ehrlich stands for the multiplicity of com- 
plements in opposition to Bordet and others who 
claim the existence of but one complement 
(alexin). The various complements differ in the 
nature of their haptophores, without regard to 
possible differences in their zymotoxic groups. 

10. Only those organs which have suitable re- 
ceptors may produce an antibody for a given anti- 
gen, i. e., only those cells which may enter into 
chemical combination with the antigen. It does 
not follow, however, that only those organs which 
shew clinical or anatomic lesions may produce, 
say, an antitoxin; for other organs not so suscep- 
tible to the action of the toxin may still possess 
the suitable receptors and cast them out as anti- 
toxin. 

Cause* of The various types of immunity are explainable 
Types* e of on the basis of the side-chain theory in the follow- 

Immunity. -^ terms . 

1. Natural immunity to toxins may depend on 
(a) a lack of suitable cell receptors, the toxin con- 
sequently finding no point of attack; (b) a very 



-NATURE OF IMMUNITY. 355 

low affinity between cell receptors and toxin so 
that the latter does not unite with the cells except 
under special conditions (e. g., the immunity of 
chicken to tetanus) ; or (c) on the presence of 
natural antitoxins. 

2. Acquired active antitoxic immunity depends 
on the multiplication and excretion of cell recep- 
tors (antitoxin) into the circulation, the new- 
formed bodies having the power of combining 
chemically with additional toxin which may be in- 
troduced. 

3. Passive antitoxic immunity, as established by 
the injection of an antitoxin, depends on the abil- 
ity of the antitoxin to combine chemically with the 
toxin and thus to divert the latter from the cells. 

4. Natural immunity to bacteria depends on (a) 
a lack of suitable cell receptors with which the 
toxic bacterial constituents might combine; (&) a 
very low affinity between cell receptors and the 
toxic bacterial constituents; or (c) on the presence 
of natural bacteriotysins (amboceptors and com- 
plements). 

5. Acquired active antibacterial immunity de- 
pends on the multiplication and excretion into the 
circulation of specific cell receptors (amboceptors) 
which have the power of uniting- with complement 
to kill the micro-organisms which may be intro- 
duced. 

6. Passive antibacterial immunity, as estab- 
lished by the injection of a bacteriolytic serum, 
depends on the ability of the amboceptors con- 
tained in the serum to unite chemically with the 
receptors of the micro-organism, as a result of 
which complement is absorbed to kill and perhaps 



356 INFECTION AXD IMMUNITY. 

to dissolve the bacteria. The complement may be 
present in the serum which is injected, or the nat- 
ural complement of the individual may be utilized 
by the amboceptors. 
comparison When one seeks to compare the theory of Ehrlich 
of Ehrlich with that of Metchnikoff, one finds little more in 

and Metcli- ,-. ,•■ , £ -, . . 

niivon. common than the general purpose 01 explaining 
the phenomena of immunity. Yet it is remark- 
able that where there is so little in common there 
are so few contradictions of an essential nature. 

The theory of Ehrlich has that degree of defi- 
niteness which it must have in order to be a plausi- 
ble chemical theory, whereas that of Metchnikoff 
seems more general in that it is so largely biologic 
and vitalistic. 

Each has a certain relation to nutrition. Phago- 
cytosis as a nutritional measure is found in lower 
types of animals, and accomplishes nothing further 
than to bring the food substance in contact with 
the digestive ferments contained in the cell. In 
relation to nutrition the theory of Ehrlich begins, 
so to say, where the phagocytic theory leaves off, 
involving, as it does, the method by which food 
substances become a part of the protoplasm. 

Metchnikoff, with Ehrlich, recognizes the vari- 
ous antibodies which have been discovered. The 
former holds that all are produced by the phago- 
cytes without suggesting clearly a method by 
which they may be formed. Ehrlich assumes a 
very precise method by which they may be formed, 
but designates no particular cells as their pro- 
ducers, stating only in a general way that an anti- 
body is produced only by those cells with which the 



THEORIES OF METCHNIKOFF. 357 

antigen may combine; in some instances, the leu- 
cocytes may be such cells. 

The theory of Metchnikoff is not concerned with 
the structure of toxins and the various antibodies, 
nor with the method by which toxins may injure 
the cells, whereas Ehrlich presents definite concep- 
tions on these points. 

Both recognize that there is more than one com- 
plement (cytase). Ehrlich recognizes no limit to 
the varieties which may exist, whereas Metchnikoff 
describes but two cytases, microcytase and macro- 
cytase. 

The view which Metchnikoff has expressed, that 
antitoxin is produced by some action of the phago- 
cytes on the toxin, is directly opposed to that of 
Ehrlich which recognizes antitoxin as a product of 
the cell itself. 

They agree that amboceptors (fixators) become 
extracellular in the blood. 

Metchnikoff holds that complements (cytases) 
are produced only by the phagocytes and that 
these substances are found in the plasma or serum 
only as a result of injury to the phagocytes (phago- 
lysis). These points are not involved essentially 
in the theory of Ehrlich. Certain investigators 
who work in harmony with the side-chain theory, 
as well as those who represent the views of Metch- 
nikoff, have extracted complement from the leuco- 
cytes. Some of Ehrlich's supporters believe that 
complement exists normally in the plasma. 

Metchnikoff and Ehrlich hold divergent views 
concerning the action of antitoxins, the former be- 
lieving that antitoxins stimulate the phagocytes to 
an increased absorption and consequent destruc- 



358 INFECTION AXD IMMUNITY. 

tion of the toxin, whereas Ehrlich claims that 
antitoxin neutralizes toxin by combining chemi- 
cally with it. 

According to Metchnikofr", all types of immunity 
depend, directly or indirectly, on phagocytic activ- 
ity. While the side-chain theory is not in har- 
mony with such a broad assumption, it carries 
with it no denial of the phenomenon of phagocyto- 
sis nor of its importance in certain infections. 
compatibility From these selected considerations it is seen 
that the two theories do not stand to each other in 
the relation of antitheses, and in the light of pres- 
ent knowledge it would seem unwarranted to cling 
to one view to the absolute exclusion of the other. 
It does not follow that because demonstrable 
serum properties explain immunity to one disease, 
or to a certain group of diseases, that recovery 
from all diseases must depend on properties of the 
serum; nor because phagocytic activity explains 
recovery in certain instances that recovery from 
all diseases must depend on a similar activity. The 
conditions which exist in each disease, of course, 
must be recognized independently. It so happens 
that recovery from a certain group of diseases, 
e. g., staphylococcus, streptococcus and pneumo- 
coccus infections, is not accompanied by the de- 
velopment of conspicuous antitoxic or bactericidal 
properties in the serum, but they are characterized 
by a great increase in the number of circulating 
leucocytes (microphages), cells of known phago- 
cytic and bactericidal power, whereas the opposite 
conditions are found in certain other diseases, e. 
g., typhoid and diphtheria. If one seeks the most 
apparent explanation in each case, the great leuco- 



OPSOXIXS AND EHRLICH'S THEORY. 359 

cytosis would seem to be of prime importance in 
the first group, and the antitoxic and bactericidal 
power of the serum in the second. 

Investigations from various sources render un- opsonins. 
questionable the value of phagocytosis in certain 
infections, and of particular significance is the 
work concerning opsonins which was referred to in 
the preceding chapter. From this work it follows 
that even for the phagocytic destruction of bac- 
teria the serum contains properties which are of 
essential importance. This appears of all the more 
importance from the fact that immunization with 
at least some micro-organisms (streptococcus, 
staphylococcus) causes an increase in opsonins or 
bacteriotropic substances. 

The accompanying illustration, with some modi- 
fications, is taken from "Ehrlich/s Seitenketten- 
ihcorie," by Ludvig Aschoff. The cell used for 
immunization is assumed to be a cell which will 
cause the formation of antitoxin, agglutinin or 
precipitin, and bactericidal amboceptors; the 
diphtheria bacillus is such an organism, consider- 
ing toxin as one of the receptors of the bacillus. 
This means that the bacillus is able to cause the 
overproduction of all three types of receptors. The 
illustration, however, is on the basis of a hypo- 
thetical cell (p. 360). 

A list of immunizing bodies, their anti-bodies, 
and synonyms for complement and amboceptor, 
is also appended (p. 361). 



IMMUNIZATION WITH ANTIBODIES. 



List of Immunizing Bodies and Their Antibodies. 

Antigens or Products of 
Immunizing immuniza- 
substances. tion. 



Toxins. 
Complements 

Ferments. 

Precipitogen- 
o u s sub- 
stances 

Agglutinogen- 
o us sub- 
stances 

Opsonigenous 
substances 
of bacteria 

Cytotoxin pro- 
ducing sub- 
stances 



Antitoxins. 
Anticomple- 

ments 
Antiferments 
Precipitins 



Agglutinins 



Opsonins 

Cytotoxins. 



("Hemolysins 
. .1 Bacteriolysins 
1 Special Cyta- 
le toxins 

Spermotoxin 
Nephrotoxin 
Hepatotoxin 
Neurotoxin 
Syncytioly- 
sin, etc. 



Consisting of 
two bodies, 
i. e., comple- 
me n t and 
amboceptor. 



Immunization with Antibodies. 



Precipitins 
Agglutinins 
Cytotoxins 

Hemolysins, 

etc. 



Complement 



Antiprecipitins 
Antiagglutinins (°?) 
Anticyto toxins 

Antihemolysins, 

etc. 



Alexin 
Cytase 



f Consisting either of anti- 
| complements or antiam- 

boceptors ; the latter 
) may be an antibody for 
\ the complementophilous 

or for the cytophilous 
I haptophore of the ambo- 
V ceptor. 



Synonyms 

Amboceptor 

Immunkorper 

Zwischenkorper „ 

Intermediary body 

Substance sensibilisatrice 

Fixator 

Preparator 

Copula 

Desmon 



CHAPTER XXII. 



PRINCIPLES OF SEROTHERAPY. 

In the strict sense serotherapy means the in- 
jection of antitoxic or antibacterial serums for 
curative or proplrylactic purposes; this is passive 
immunization or direct serotherapy. Active im- 
munization, in which the tissues of the individ- 
ual are induced to form antitoxins or antibacterial 
substances as a result of vaccination or protective 
inoculations, may be considered as indirect sero- 
therapy. We may, therefore, include the latter as 
one of the serotherapeutic measures. 

Bearing in mind the significance of the terms 
active and passive immunization, and the fact 
that they may be used for curative and prophylac- 
tic purposes, the various procedures may be classi- 
fied as follows:* 

I. PROPHYLACTIC INJECTIONS. 

classification A. Active immunization, in which vaccina- 
npentic Mens" tion and protective inoculations are included, as 
s ' with the organisms of typhoid, cholera and plague. 
Depending on the material injected, the result is 
the formation of antitoxins or antimicrobic sub- 
stances (amboceptors) ; agglutinins are formed in- 
cidentally. 

1. Inoculation of virulent organisms, (a) In- 
oculation with small amounts of a virulent organ- 
ism, i. e., of a non-fatal dose; used principally in 
experimental work, (b) Inoculation with virulent 

* Modified from Deutsch and Feistmantel in "Die 
Trnpfstoffe und Heilsera," Leipsic. Geo. Thieme, 1903. 



nrei 



SEROTHERAPEUTIG MEASURES. 363 

organisms into a tissue which has some natural re- 
sistance. The success of vaccination against small- 
pox by using virus obtained directly from the dis- 
eased, a method which was practiced in earlier 
times, was probably due to the fact that the virus 
found unfavorable conditions for the development 
of virulence in the skin. In some instances im- 
munization is accomplished more successfully by 
inoculation of bacteria or toxins into the blood 
stream, as in Kitf s method of vaccination against 
symptomatic anthrax and in immunization with 
rattlesnake venom. 

2. Injection of attenuated virus or toxin. At- 
tenuation may be accomplished by air and light 
(chicken-cholera, Pasteur) ; by cultivation at high 
temperatures (anthrax, Pasteur) ; by chemical 
agents (anthrax, Eoux; diphtheria and tetanus 
toxins, Behring and Eoux) ; by desiccation (rabies, 
Pasteur) ; by passing the virus through other 
animals (swine erysipelas, Pasteur). This last 
observation was a most instructive one; passing 
the bacillus through the rabbit several times in- 
creased its virulence for the rabbit but decreased it 
for swine, while passing the organism through the 
dove increased its virulence for swine. 

3. Injection of killed organisms (anthrax, Tous- 
saint; swine plague, Salmon and Smith). This 
is the safest means of vaccinating against cholera, 
typhoid and plague. In the Pasteur treatment of 
hydrophobia the first injection of the dried spinal 
cord probably contains the killed virus. 

4. Injection of bacterial constituents (a) Bacter- 
ial cell plasm (Buchner's plasmin, obtained by sub- 
mitting micro-organisms to high pressure, and 
Koch's tuberculin TE) ; (b) Soluble bacterial 



3G4 INFECTION AXD IMMUNITY. 

products (the bacterial proteins, as Koch's old 
tuberclin and mallein; the soluble toxins; 
products of bacterial autolysis). When toxins 
are injected antitoxins are formed. The 
autolytic products of some organisms, e. g., 
typhoid and dysentery, cause the formation of bac- 
tericidal amboceptors and agglutinins, but not 
antitoxins. 

B. Passive immunization: the prophylactic in- 
jection of antibacterial and antitoxic serums. 

C. Mixed active and passive immunization: the 
simultaneous injection of an immune serum with 
the corresponding organism, which may be killed 
or living. The serum causes immediate, though 
temporary, resistance, and, in the meantime, an 
active, more permanent immunity develops as a 
consequence of the injection of the organ.'sms. 
This method has been practiced with swine plague, 
swine erysipelas, rinderpest, and experimentally 
in typhoid, cholera and plague. 

II. CURATIVE INJECTIONS. 

A. Active immunization. 

1. Injection of killed micro-organisms in small 
doses with the intention of hastening antibody for- 
mation, as suggested by Fraenkel in the treatment 
of typhoid fever ; value not yet demonstrated. 

B. Passive immunization. 

1. With antitoxic serums: diphtheria, tetanus, 
snake bites, plague, tuberculosis (?), typhoid (?), 
streptococcus infections (?), etc. 

2. With antibacterial serums: typhoid, cholera, 
plague, dysentery, streptococcus (?), staphylococ- 
cus ( ?) and pneumococcus ( ?) infections. 



STRENGTH OF SERUMS. 365 

In general, serums to be effective must have a General 
certain strength. When diphtheria antitoxin was serums. 
first used preparations were put on the market 
which contained twenty or fewer antitoxin units 
per cubic centimeter, a strength which would 
necessitate the injection of 150 c.c. or more in or- 
der to introduce 3,000 units. Much of the early 
criticism of diphtheria antitoxin is traceable to the 
low value of the serums used at that time rather 
than to an injurious effect on the patients. If 
diphtheria antitoxin now contains less than 250 
units per c.c. it is considered unfit for use; many 
serums contain 500 or more units per cubic cen- 
timeter. 

Antitoxic and other serums should be free from 
micro-organisms and toxins. The cases of tetanus 
which developed in St. Louis following the injec- 
tion of diphtheria antitoxin will be remembered. 
With correct governmental supervision of the 
manufacture of serums, such accidents are entirely 
preventable. 1 

For the sake of simplicity we may consider the 
principles involved in serum therapy under the 
three topics of (a) antitoxins, (b) bactericidal or 
antibacterial serums, and (c) vaccination. 

(a) antitoxins. 
It has been sufficiently emphasized that neutral- Antitoxins. 
ization of toxin by antitoxin implies a chemical 
union between the two substances. When the two 
are mixed outside the body at a given temperature 
and at a given concentration, the rapidity and com- 
pleteness with which the union occurs depends 
only on the degree of affinity which one has for the 

1. See Chapter XI (Part II). 



366 INFECTION AND IMMUNITY. 

other. There is no third substance with which one 
or the other may unite. In the bocty, however, the 
conditions are more complex ; in this case two com- 
binations are possible for the toxin, one with the 
antitoxin which has been introduced and a second 
with the tissue cells. As an instance of the great 
rapidity with which toxin may unite with cells, 
the work of Heymans with tetanus toxin may be 
cited. "Heymans found that, if all the blood were 
removed from an animal a few minutes after the 
injection of a single fatal dose of tetanus toxin 
and the blood of another animal substituted, still 
the animal died of tetanus" (Ritchie) ; that is to 
say, all the toxin had been bound by the cells in 
that brief time. 
Binding of Other experiments show that quantities of toxin 
Tissues, and antitoxin which are neutral when mixed be- 
fore injection are not entirely neutral if injected 
separately and at different points of the body. In 
this instance some of the toxin has had time to 
unite with tissue cells before it could come in con- 
tact with the antitoxin. 

Certain work by Donitz illustrates not only the 
rapidity with which toxin may be bound by the 
tissue, but also the method by which antitoxin ef- 
fects a cure. In relation to tetanus he found that 
if the toxin were injected first and the antitoxin 
four minutes later, a quantity of antitoxin, which 
was slightly in excess of the neutralizing dose, was 
required to prevent the development of tetanic 
symptoms; if he waited eight minutes, six times 
as much antitoxin ; after sixteen minutes, twelve 
times as much; after one hour, twenty-four times 
the simple neutralizing dose was required. A few 
hours later no amount of antitoxin could save the 



CURATIVE ACTION OF SERUMS. 367 

animal. Similar conditions were met in the neu- 
tralization of diphtheria toxin by its antitoxin in 
the body. Madsen, in performing what he called 
"Curative Experiments in the Keagent Glass/' 
found that the longer tetanolysin had been in con- 
tact with erythrocytes, the more antitetanolysin 
was required to tear away the toxin from the cor- 
puscles. Practical experience with diphtheria also 
indicates that the longer the disease lasts the more 
antitoxin is required for cure. 

The experiments just cited give us a clear con- 
ception as to what is meant by the curative action 
of an antitoxin — an action which consists not of 
the neutralization of the circulating toxin, but of 
the wresting away from the tissue of the toxin 
which has been bound. Incidentally the circulat- 
ing toxin is neutralized, and for this step, which 
is essentially prophylactic in nature, the simple 
equivalent of antitoxin is required. But for the 
wresting of toxin from tissue cells not a mere 
equivalent of antitoxin, but a great excess, is re- 
quired, as shown by the experiments of Donitz and 
of Madsen. 

When diphtheria or tetanus has advanced so far curatfve** 
that no amount of antitoxin will effect a cure, the Action. 
relation of the toxin to the cells has become some- 
thing more than mere chemical union. Further 
processes of a biologic or biochemic nature have set 
in in which the toxin may have become an integral 
part of the protoplasm, and the toxophorous group 
may have begun its destructive action, whatever 
the nature of this action may be. 

It is important to recognize that antitoxin can 
not repair an injury already done by the toxin. 
The repair of the injury depends on the recupera- 



3GS INFECTION AND IMMUNITY. 

live power of the cells; hence, antitoxin cures by 
tearing from the cells, perhaps not all, but so much 
of the toxin that less than a fatal dose remains in 
the cell. 
Tv taiit In pr?n" ^ e ma y l earn from the experiments of Donitz 
dpies. and of Madsen two important principles of anti- 
toxic therapy : First, that of early administration, 
i. e., before a fatal amount of toxin has been 
bound, and, second, the necessity of injecting suffi- 
cient quantities of antitoxin. 

The comparative study of diphtheria and tet- 
anus has clarified the principles of antitoxic 
therapy to no small degree.. Knowing that diph- 
theria antitoxin has a much greater curative value 
than tetanus antitoxin, we find some conditions 
which would seem to explain the difference, at 
least in part. 
Tetanus. In regard to tetanus we have the following 
facts: In the test-glass the affinity between the 
toxin and antitoxin is rather weak, since approxi- 
mately forty minutes are required for complete 
neutralization (Ehrlich). On the other hand, the 
experiments of Donitz and of Heymans show that 
the affinity of the toxin for nervous tissue is ex- 
ceedingly strong, all the toxin being taken up 
within a few minutes. These two conditions alone 
suggest the probability of a low curative value on 
the part of the serum. The toxin of tetanus also 
has a remarkable selective action on the most vital 
of all organs, the central nervous system; hence, a 
lower grade of injury may prove fatal than in 
other infections in which less important organs or 
those of greater recuperative power are involved 
chiefly. Furthermore, it seems (Meyer and Ean- 
som, Marie and Morax) that the tetanus toxin is 



DIPHTHERIA. 369 

taken up by the nerve endings and reaches the 
ganglionic cells by way of the axis cylinders, 
whereas the antitoxin which is injected remains 
chiefly in the blood and lymphatic circulations. 
Hence, the toxin, to a certain extent, is isolated 
and less accessible to the action of the antitoxin. 

Concerning diphtheria, the affinity between Diphtheria. 
toxin and antitoxin is relatively strong, for com- 
plete neutralization in the test-glass takes place in 
about fifteen minutes (Ehrlich). On the other 
hand, clinical experience indicates that the affinity 
of diphtheria toxin for tissue cells is less than that 
of tetanus toxin, for diphtheria may readily be 
cured on the second or third day of the disease, 
whereas a cure of tetanus is rarely affected. These 
would seem to be favorable conditions for success- 
ful serum therapy. Although the toxin of diph- 
theria may attack the nervous system, the paraly- 
sis seen in such cases is seldom fatal. On the basis 
of anatomic findings in fatal cases it seems prob- 
able that the greater portion of the toxin is taken 
up by parenchymatous and lymphatic organs, and 
by connective tissues (animal experiments), which 
compared with the nervous tissue are of less imme- 
diate importance for life and have greater recuper- 
ative powers. We may infer from clinical experi- 
ence that diphtheria toxin is so situated in the 
body that it is accessible to the action of the anti- 
toxin. 

We have, therefore, the following factors important 
which apparently are of importance for the sue- to" iaccels. 
cess of antitoxic therapy: 1. The concentration 
(strength) of the antitoxin which is injected. 2. 
Its freedom from contamination and adventitious 
toxins. 3. The time of its administration. 4. The 



370 INFECTION AND IMMUNITY. 

quantity injected. 5. The degree of affinity be- 
tween toxin and antitoxin. 6. The degree of affinity 
between toxin and tissue cells. 7. The amount of 
toxin which may be bound without a fatal issue, of 
which the vital importance of the organs involved 
and their recuperative powers are factors. 8. The 
location of the toxin in the body, i. e., its accessi- 
bility for the antitoxin. 
Prophylactic What has been said relates to the curative ac- 
\ntitovin. tion of antitoxin. It is evident that the action of 
antitoxin, when used as a prophylactic, is of a 
simpler nature, for in this instance the conditions 
approximate those of the test-tube experiment. 
There has been opportunity for the antitoxin to 
become uniformly distributed in the blood and 
lymphatic circulations; hence, it is able to meet 
and to bind the toxin before the latter comes in 
contact with the receptors of important cells. The 
high value of tetanus antitoxin as a prophylactic, 
a value which has become evident in recent years, 
probably depends on this condition. 

The immunity which is afforded by a prophy- 
lactic injection of antitoxin is of short duration, 
from two to three weeks; the antitoxin is excreted 
in the urine to a considerable extent, but in part 
may be bound and assimilated by the tissues. 

(b) bactericidal or antibacterial serums. 

Bactericidal Attention has been directed repeatedly to a 
large group of organisms the toxic constituents of 
which are integrally associated with the proto- 
plasm of the microbes; the toxic substances are 
endotoxins. Certain members of this group, of 
which the typhoid, paratyphoid, colon and dysen- 
tery bacilli and the vibrio of cholera are represent- 



Sermns. 



BACTERICIDAL SERUMS. 371 

atives, cause the development of strong bacterici- 
dal serums in the immunized animal. In Chapter 
XVI, A, it was shown that such serums have no 
power of neutralizing the endotoxins of the corre- 
sponding organisms; hence, whatever prophylactic 
and curative properties they may have would seem 
to depend on the bactericidal action of the ambo- 
ceptor-complement complex. As to whether the 
substances which stimulate phagocytosis, i. e., the 
opsonic or bacteriotropic substances are of impor- 
tance for the intra vitam action of bactericidal 
serums, remains to be definitely established. 

It is common knowledge that bactericidal curative 
serums have not been successful curative agents, fac'tic Power. 
although in test-glass experiments they may be 
able to kill large numbers of organisms. Experi- 
mental work has brought to light a number of con- 
ditions which render their ineffectiveness some- 
what intelligible, but this knowledge has been of 
little service in increasing their value, and at this 
moment their outlook as curative agents is not very 
encouraging. 

Animal experiments indicate that, prophylacti- 
cally, they are much more powerful than when 
used as curative agents. Unfortunately, however, 
as in the case of antitoxins, the immunity which is 
conferred is of short duration, the serum being ex- 
creted or the antibodies destroyed within two or 
three weeks. For this reason they are not suited 
for general prophylactic use in man, but they may 
be distinctly useful when combined with vaccina- 
tion, as indicated later. 

Bactericidal serums are efficient in saving ex- Time of 
periment animals, provided the serum is injected 
in advance of, simultaneously with or very shortly 



372 INFECTION AXD IMMUNITY. 

after the bacteria are introduced. By injecting 
the vibrio of cholera and anticholera serum simul- 
taneously one may readily save a guinea-pig from 
ten times the fatal dose, or more. If the culture 
be injected first and the serum later a larger 
amount of serum is required to save the animal. 
After a few hours a sufficient amount of serum to 
kill all the vibrios may be injected, yet the ani- 
mal will die from the action of the endotoxins 
which have been liberated. The organisms had 
proliferated to such an extent that the mass, 
though dead, contained a fatal amount of endo- 
toxin. A statement made previously may be re- 
peated, that the administration of a bactericidal 
serum rather than being beneficial may actually be 
injurious, in that it 'dissolves the micro-organisms 
rapidly, thereby liberating an excessive amount of 
endotoxin, this, perhaps, is not definitely estab- 
lished as a point of practical importance. 

Having determined the amount of a bactericidal 
serum which is able to save a guinea-pig from an 
incipient infection, one may calculate on the basis 
of weight the amount which would be required to 
save a man under the same conditions; frequently 
it amounts to impossible quantities, hundreds of 
cubic centimeters. The conditions are all the less 
promising when we remember that physicians are 
usually called on to treat well-established rather 
than incipient infections. 
Peculiarities Other conditions which operate against the ef- 
ment and fectiveness of bactericidal serums as curative 
ceptois. a g en | s j iave -|- ^ w ^li peculiarities of comple- 
ments and amboceptors. The lability of comple- 
ment involves certain difficulties. A bactericidal 
serum, as one would purchase it, contains none, 



ANTIBACTERIAL SERUMS. 373 

because of its spontaneous degeneration. Theo- 
retically, this difficulty may be obviated in three 
ways : First, one may use serums which are fresh 
from the immunized animal ; second, one may com- 
plement the solution of amboceptors (old immune 
serum) by the addition of fresh serum from a nor- 
mal animal which is known to contain suitable 
complement ; or, third, one may inject the comple- 
ment-free serum and place reliance on the comple- 
ment which exists in the plasma and lymph of the 
patient for activation of the amboceptors. It is 
sufficiently established that none of these proce- 
dures enhances the curative value of the serums to 
a satisfactory extent. ■ 

Kegardless of the amount of foreign comple- Absorption 
ment which is introduced, it appears to be di- meSt™? 1 * 5 " 
verted from its function. It has been shown ex- tlie Tissues - 
perimentally that the tissues may absorb a foreign 
complement, and the mere fact that anticomple- 
ments are formed so readily indicates that comple- 
ment may be bound by the tissues. In accordance 
with a rather general principle, if the animal 
which furnishes the serum is remote from man 
zoologically there is all the more likelihood of the 
complement being fixed by human tissues. 

It has been suggested that if one should choose choice of 
for immunization animals which are closely re- for immani- 
lated to man, as chimpanzees and monkeys, a 
double advantage would be gained : First, the for- 
eign complement may be identical or similar to 
that in man and consequently would be less likely 
to be absorbed by the tissues; and, second, the 
complementophilous haptophores of the ambocep- 
tors may be so constructed that human comple- 
ment would serve for activation. Theoretically, 



374 INFECTION AND IMMUNITY. 

the conditions would be ideal if immune human 
serum were available for therapeutic purposes. 

If one depends on the complement in the pa- 
tient's body for activation of the amboceptors, 
there are two possible difficulties of importance: 
First, the native complement of the body is often 
decreased during infections and in some chronic 
diseases and may be too little for thorough activa- 
tion; second, the amboceptors of the immune 
serum may demand for their activation a comple- 
ment or complements which the body does not con- 
tain. 
Diversion of Diversion of complement has been referred to as 

Complement. . , , , . , T 

a phenomenon seen in test-tube experiments. In 
this condition an excess of amboceptors in some 
way decreases the power of the serum; by an ex- 
cess of amboceptors one means, in this instance, 
such a quantity that many are unbound by the 
bacteria. It is supposed that a certain amount of 
the complement is absorbed by free or unbound 
amboceptors, hence the effect is like that of too 
little complement. In the desire to administer a 
sufficient amount of antibodies, so much may be 
introduced that diversion of the complement oc- 
curs in the body. Results obtained by Loffler and 
Able, by Pfeiffer and by Buxton and others, in 
which excessive doses of immune serum were less 
protective than moderate doses, show that a simi- 
lar phenomenon occurs in the body. 
inaeeessiMi- j n certain diseases the microbes are so situated 

lty of Mi- 
crobes, that a serum as ordinarily administered may not 

be able to reach them. Pfeiffer thinks that there 
is little hope for the serum treatment of cholera 
because of the exclusive location of the living or- 
ganisms in the intestinal tract. In typhoid also 



ANTIBACTERIAL SERUMS. 375 

the intestines are a reservoir of typhoid bacilli, 
although the living organisms reach the circula- 
tion in abundance. 

By way of summary, the following conditions 
appear as factors in the low curative value of bac- 
tericidal serums: 1. Bactericidal serums are not 
antitoxic. 2. They may liberate an excessive 
amount of endotoxin by dissolving the bacteria. 3. 
The lability of exogenous complement. 4. The 
power of the tissues to absorb the complements of 
a foreign serum. 5. The lack of a sufficient 
amount of suitable complement in the human 
body. 6. The difficulty of obtaining amboceptors 
for which human complements are suited. 7. The 
possibility of diversion of complement by an ex- 
cess of amboceptors. 8. Inaccessibility of the 
micro-organisms in certain infections (cholera, 
typhoid). 

As pointed out elsewhere, another group of or- other "Anti 

*■ ?• o x bacterial" 

ganisms, the members of which contain endo- serums. 
toxins, causes the formation neither of antitoxins 
nor of bactericidal serums; streptococcus, staphy- 
lococcus, pneumococcus, etc. Many investigators, 
nevertheless, are positive in their claims that the 
antiserums for these organisms have a protective 
and even a curative value. The properties on which 
their value depends have not been satisfactorily 
ascertained. Although certain antistreptococcus 
serums are said to be antitoxic, it is contended by 
others that they act by stimulating phagocytosis. 
It has been shown that immunization with these 
organisms causes an increase in the opsonins. 
Their curative value is very low in experimental 
work and they fail totally if injected a few hours 



376 



INFECTION AXD IMMUNITY. 



subsequent to the introduction of the organisms. 
Clinically, we are familiar with them as failures. 

It is particularly in relation to the streptococ- 
cus that the so-called polyvalent serums have been 
prepared. Cultures of streptococcus obtained 
from numerous sources are used in the immuniza- 
tion with the expectation that the serum will be 
effective against various strains of streptococci. 
The principle may be an important one in the 
preparation of other antibacterial and bactericidal 
serums. 

(C) VACCINATION. 
A r accination We are most familiar with the terms vaccine 
° r inocuiaUon. and vaccination as applied to protective inocula- 
tion against smallpox. They are used, however, 
with equal propriety in all instances in which the 
attenuated or killed virus of a disease is inoculated 
for the purpose of establishing resistance to an 
infection. The process set in motion by vaccina- 
tion is one of active immunization in which the 
cells are induced to form specific antibodies over a 
long period; hence, the resistance is more pro- 
tracted than that established by passive immuni- 
zation. 

Certain experimental work, as previously stated, 
indicates that the acquired resistance persists after 
the formation of antibodies has ceased, even after 
the quantity of the latter has sunk to the normal. 
This condition has been explained by assuming 
that, as a consequence of vaccination, the cells of 
the body have been "trained" to produce the cor- 
responding receptors; hence, when the micro-or- 
ganisms gain entrance at a subsequent time new 
antibodies are formed so rapidly and in such abun- 
dance that the incipient infection is overcome. 



NEGATIVE AND POSITIVE PHASES. 377 

In some instances the nature of the virus used 
is unknown, as in smallpox and hydrophobia; in 
all probability, however, it consists of micro-or- 
ganisms rather than of toxins alone. In the case 
of typhoid, cholera, plague and other diseases of 
known etiology pure cultures, living or killed, are 
inoculated. Protection does not follow immedi- 
ately on the inoculation. We are sufficiently fa- 
miliar with this fact in relation to smallpox, in 
which several days are required for the formation 
of a protective amount of the antibodies. There 
is reason to believe that the interval between the 
inoculation and the appearance of antibodies is 
characterized by a decreased resistance on the part 
of the individual, so that during this brief period 
he is unusually susceptible to infection. 

That period immediately following the injec- J es *"y e and 
tion of a toxin or microbe, in which the quantity Phases. 
of antibodies undergoes a temporary decrease, 
Wright speaks of as the negative phase of the im- 
munization; whereas that period marked by the 
new formation of antibodies is called the positive 
phase. The negative phase lasts from a day or 
two to several days, depending on the quantity and 
nature of the virus injected (typhoid). A second 
injection should not be given during the negative 
phase, since it causes a further decrease in the 
antibodies and prolongs the phase. Wright speaks 
of this as a cumulative negative phase. A cumu- 
lative positive phase, marked by the formation of 
larger amounts of antibodies, may be induced by 
the proper spacing of a number of injections. 

In certain instances the nature of the anti- Nature of 
bodies is known. In typhoid, cholera, plague and 
dysentery, for example, they consist of bactericidal 



378 



INFECTION AND IMMUNITY. 



Mixed Active 

and Passive 

Immunization. 



amboceptors; agglutinins and precipitins are 
formed incidentally. The amboceptors naturally 
depend on the complement of the body for their 
activation. If the disease is one of unknown etiol- 
ogy the nature of the antibodies is not easily de- 
termined. We should keep in mind the possibil- 
ity that vaccination may cause an increase of the 
opsonins and that the potential phagocytosis may 
thereby become greater. 

In case the incubation period of the vaccination 
is shorter than that of the disease (smallpox, hy- 
drophobia) vaccination usually is successful even if 
practiced within a limited time after exposure to 
infection. 

Vaccination in individual diseases is considered 
in Part II. 

Theoretically it would be possible to immunize 
man against diphtheria and tetanus by inoculating 
with small amounts of the corresponding toxins. 
Such a procedure, for obvious reasons, would be 
unnecessary and unjustifiable. 

It is not unlikely that mixed active and passive 
immunization will be of great service in some in- 
fections. A successful campaign against rinder- 
pest has been carried on in the Philippines by this 
method. The blood of infected cattle contains the 
virus, which as yet has not been cultivated artifi- 
cially. The serum of cattle which have recovered 
from the disease, or which have been immunized 
cautiously with infected blood, contains the speci- 
fic antibodies. Both the immune serum and viru- 
lent blood are used for the inoculations. The same 
principle has been found effective in experimental 
work with cholera, typhoid and plague. Immedi- 
ate immunity is established by the serum, which 



CURATIVE VACCINATION. 379 

would eliminate the danger period mentioned 
above, and before the serum disappears entirely 
active immunity develops. 

Wright, following his observations on the varia- £. ura * iv « 
tions in opsonic power of the serum in different 
infections, concluded that in certain localized 
chronic infections such as chronic suppurative 
processes, the body as a whole did not respond to 
the infection with the production of antibodies. 
The injection of dead homologous organisms was 
therefore resorted to in order, in the words of 
Wright: "To exploit in the interests of the in- 
fected tissues, the unexercized immunizing capac- 
ities of the uninfected tissues." 

The dosage of the injected vaccine was de- 
termined according to the purpose of using the 
minimum quantity which would result in the 
maximum response of the uninfected tissues with 
the least development of the so-called negative 
phase. In order to* regulate the frequency and 
size of the therapeutic inoculations, Wright made 
use of opsonic index estimations. 

Vaccines are prepared as follows : 

The desired organism is grown on a suitable 
solid medium as an agar slant or blood serum 
slant for the minimum time required for a good 
growth, usually twenty-four hours. 

Salt solution is then added to the slant, a few 
cubic centimeters are usually sufficient for an 
ordinary growth (the quantity need not be exact), 
and the culture scraped off into the salt solution 
with a sterile glass rod or platinum loop. The 
number of bacteria per cubic centimeter is then 
estimated by mixing equal volumes of defibrinated 



380 INFECTION AND IMMUNITY. 

blood and bacterial suspension and then diluting 
and smearing on a slide. The dilution should be 
about five times. The method of measuring equal 
small volumes by means of capillary tubes as 
given in Chapter XIX, may be used and a 
Eomanowski stain used for staining. 

Since the number of corpuscles in normal 
human blood is about 5,000,000, by a comparison 
of the number of bacteria with the number of 
corpuscles the number of bacteria per cubic cen- 
timeter can be readily estimated. By dilution with 
salt solution the required dosage per cubic cen- 
timeter may be obtained. When it is necessary to 
keep the vaccine a small amount of tri-cresol (.2 
per cent.) may be added. 

Eecently therapeutic inoculations have been used 
for a great variety of infections, both acute and 
chronic, and to both local and systemic infections. 
Naturally, the results have also varied within wide 
range. 

In case of chronic localized infections the 
theoretical basis for the use of vaccines seems 
plain. As pointed out by Theobald Smith : "The 
effectiveness of vaccines applied in the course of 
acute febrile diseases, such as typhoid fever and 
pneumonia must be accounted for by principles of 
which experimental medicine has as yet no definite 
knowledge." Theoretically no advantage can be 
expected from adding toxins in an already over- 
intoxicated case. 

This criticism does not apply, of course, to such 
a procedure as is suggested by Eosenow. (See chap- 
ter on Pneumonia.) 



CHAPTER XXIII. 



ANAPHYLAXIS. 

Attention has already been called to the fact 
that an individual may be more susceptible to 
infections at one time than at another through 
various accidental conditions, as exposure and 
exhaustion. This, however, is not a specific lryper- 
susceptibility and is usually more or less transient. 

In contrast to this accidental condition, stands 
a specific susceptibility which is now commonly 
known as anaphylaxis. The condition of the in- 
dividual or animal is spoken of by V. Pirquet as 
allergy (AUergie), a word which conveys the idea 
of an altered power of reaction on the part of the 
animal body. 

V. Pirquefs conception of allergy is best de- 
scribed in his own words, in which he uses vac- 
cination and revaccination as an illustration. 
"Vaccinia, with which we can at any time institute 
an infection, is just as much an infectious disease 
as is variola, of which it represents an attenuated 
form. Let us inoculate one person who was 
vaccinated two years previously and who, accord- 
ing to the customary view, is immune, with a 
drop of lymph. Then inoculate another who has 
not gone through this process and attend it 
closely. Now will the immune person show ab- 
solutely nothing? On the contrary, when we re- 
turn after 24 hours, we find in the one who 
received his first inoculation (the normal person), 
a small crust showing no reaction, while in the 



382 INFECTION AND IMMUNITY. 

immune there is a normal small, raised, inflam- 
matory, itching, hyperemia area. 

"Is the one previously inoculated, therefore, 
hypersusceptible ? If we wait a few days the 
picture changes: The papule becomes brownish 
and smaller, while in the case of the first vaccina- 
tion, a vesicle forms under the crust, which in- 
creases more and more, becomes surrounded by a 
wide zone, and leads to a pustule. Now we must 
conclude that the one receiving his first inocu- 
lation is the more susceptible, since he has fever, 
pain, and a marked local inflammation, while in 
the immune person signs of infection have long 
since disappeared. 

"As it appears to me both individuals have 
reacted: The one earlier, the other later; one 
with a papule, the other with a pustule. In one 
the reaction was hardly noticeable, in the other 
pronounced. Through the previous inoculation 
no immunity in the sense of insusceptibility has 
developed, but it is only the ability to react which 
has changed, and this in point of time, quality, 
and quantity." 

The condition then appears to be a paradoxical 
one, in that we have a certain degree of hyper- 
susceptibility in a person who is really immune 
and his immunity may depend to a greater or 
less degree on his ability to react quickly to the 
presence of the infectious agent before the latter 
has time to proliferate extensively. 

Portier and Eichet, in 1902, observed a peculiar 
behavior on the part of a poison found in certain 
actinia. 



ANAPHYLAXIS. 383 

The poison was invariably fatal for dogs when 
given as a first injection in closes of 0.8 gm. per 
kilogram of animal weight, but was rarely fatal 
in closes of under 0.2 gm. per kilogram. Death 
usually occurred in from four to nine days. When 
a second dose, however, was given to an animal 
which had recovered from the first injection, 
death supervened in a short time, usually within 
two and three-quarters hours. The first injection 
evidently modified the resistance of the animal in 
some way so that it became more susceptible to 
the poison than it was in the first instance. It 
was to this modified state of the animal's resist- 
ance that Eichet applied the name "anaphylaxis," 
which stands in contrast to a condition of pro- 
phylaxis. 

In 1903, Arthus observed that, when rabbits Arums' piie- 
had received several injections of horse serum at 
intervals of several days, the serum ceased to be 
absorbed as at first and that there resulted local 
necrosis and often sloughing with subsequent ulcer 
formation. 

In 1904, Theobald Smith told Ehrlich of a Theobald 
phenomenon which he had observed while testing phenomenon, 
the potency of diphtheria antitoxin on guinea- 
pigs. Animals which had received injections of 
antitoxic horse serum and later were injected with 
a small quantity of normal horse serum became 
acutely ill or died. 

In the following year, 1905, appeared the ar- 
ticles of Otto, Eosenau and Anderson, and of v. 
Pirquet and Schick. Since these articles an 
enormous amount of work has been clone to cor- 



INFECTION AND IMMUNITY. 



Natural 

Anaphylaxis. 



relate the phenomena of anaphylaxis with other 
processes of immunity. 

Like other processes of immunity anaphylaxis 
may be classified as natural and acquired; and, 
again, acquired anaphylaxis may be active, in 
which the process results from a reaction on the 
part of the tissue cells, or may be passive — result- 
ing from the introduction of ready-made sub- 
stances into the body. 

It has been long known that, as noted by 
Horwitz, Schofield, Doerr, and others, certain in- 
dividuals are unusually affected by the ingestion 
of eggs, crabs, flesh, pork, etc. The symptoms 
are variable, but there is often nausea, fever, colic, 
and exanthemata. It is of course to be questioned 
as to whether such hypersusceptibility is really 
natural or acquired by early sensitization. Scho- 
field reports such a case of hypersusceptibility to 
egg which disappeared after repeated increasing 
closes of egg taken in pills, using minute amounts 
to begin with. Such hypersusceptibility has been 
long known under the name idiosyncracy. The 
idiosyncracies to proteins, however, should be dis- 
tinguished from those in which known chemical 
substances, such as mercury or salicylic acid, are 
concerned. 

Active anaphylaxis has been studied in a variety 
of mammals and fowls, and substances which 
correspond to those concerned in immunization 
have been demonstrated. 

It will be well to take up these various factors, 
and after a discussion of their nature, it will be 
easier to understand the theories concerning the 
mechanism of their action. 



ANAPHYLAXIS. 



385 



The sensitizing agent in anaphylaxis has re- Antisem. 

ceivecl the name of anaphylactogen, or sensibili- 
sinogen, and ma}' be defined as any substance 
which, when taken into the body, produces a 
specific hypersusceptibility, usually after an incu- 
bation period of at least from five to seven days. 

The substances which have been demonstrated 
to act as anaphylactogens are proteins or are in- 
separably connected with proteins. That anaphy- 
lactogens are closely related, or, as Friedberger, 
Doerr, and others think, identical with those 
bodies which produce complement deviation, anti- 
bodies, and precipitins, is shown by the fact that 
the same substances produce all three phenomena. 
Thus, as with precipitinogens we have an anaphy- 
laxis specific for species and for tissues. The 
same tissues which are specific for precipitin for- 
mation, c^talline lens, spermatozoa, and placenta, 
also give a specific anaphylaxis, while those tissues 
such as kidne}^, liver, etc., which produce only 
species specific precipitins produce species specific 
anaphylaxis. As an exception to this rule, it may 
be mentioned that Wells does not find that iodized 
albumin produces anaplrylaxis specific for iodized 
albumins rather than species, specific reactions, as 
was found for precipitins by Obermayer and Pick. 

One of the first questions which arose concern- Relation t<r 
ing Theobald Smith's phenomenon was that of the Toxicity. 
relation of the anaphylactogen to the diphtheria 
toxin and antitoxin. In this case, the employment 
of normal horse serum readily showed that an- 
aphylaxis was independent of the diphtheria bacil- 
lus derivatives and antitoxin present in the serum. 



386 INFECTION AND IMMUNITY. 

Somewhat more difficult is the question regard- 
ing the primary toxicity of such substances as are 
contained in eel serum, various phytalbumins and 
bacteria. It has been shown by Doerr and Rau- 
bitschek that by heating or by acidifying eel serum 
it is possible to remove the primary toxicity with- 
out taking away the property of producing anaphy- 
laxis. In a similar way it has been shown by 
Eosenau and Anderson, Vaughan, and others, that 
bacterial proteins free from toxic action can pro- 
duce anaphylaxis. It has also been shown that 
whereas in primarily toxic serum the larger the 
dose the greater the toxicity, in anaphylaxis sensi- 
tization smaller doses sensitize more readily than 
large ones. 

That hypersusceptibility to true toxins does oc- 
cur, however, has been demonstrated in the case of 
diphtheria toxin and tetanus toxin. The phe- 
nomena here, however, are distinct from anaphy- 
laxis in the fact that the incubation period is 
absent, that the symptoms come on gradually after 
the second dose, and lastly, that after a certain 
length of time which corresponds to the incuba- 
tion time of anaphylaxis, immunity or decrease in 
susceptibility, occurs in contrast to anaphylaxis. 
We must conclude, then, that toxicity and sensi- 
tizing properties are distinct from each other. 
sensitization The anaphylactogen comes into consideration in 
the primary or sensitizing dose and in the second- 
ary or toxic dose. Many experiments have been 
carried out to determine whether or not the sen- 
sitizing and toxic action are dependent on the 
same substance or similar qualities of the same 
substance. It was found, for instance, that in the 



ad Toxicity. 



SENSITIZATION AND TOXICITY. 387 

case of egg albumin one twenty millionth of a 
gram sufficed for sensitization (Wells), and about 
one thousand times that amount was required for 
a toxic dose. It was also found that by heating 
to 90° or 100° C. it became much more difficult 
to cause intoxication in sensitized animals than 
to sensitize them. Besredka concluded from these 
experiments that sensitizing and toxic substances 
were distinct from each other. Vaughan and 
Wheeler by digestion with hot absolute alcohol and 
sodium hydrate obtained a separation of albumin 
into two parts, one of which showed a marked 
sensitizing property and but little toxicity (alcohol 
insoluble portion) ; the other portion (alcohol 
soluble), a more highly toxic action. They con- 
cluded that toxic and sensitizing substances were 
present in the same molecule and that by their 
process a splitting of the molecule into toxic and 
sensitizing groups was obtained. 

The work of Vaughan and Wheeler was done 
on whole egg white and other crude proteins. 

Wells, working with pure crystallized albumin, 
obtained toxic and sensitizing action in this w r ay 
in quantities smaller than those represented by 
Vaughan's minimum sensitizing and toxic split 
products. It seems possible, therefore, that by the 
process of Vaughan and Wheeler amounts of pro- 
tein too small to produce toxic effects, but capable 
of sensitizing, escaped splitting through alcohol 
precipitation wlaile the alcohol soluble portion con- 
sisted of toxic split products. The action of heat 
may be due to the fact that both toxic and sensi- 
tizing substances are equally influenced, but that 
the apparent effect is greater on toxicity because 



388 INFECTION AND IMMUNITY. 

for intoxication larger amounts are necessary than 
for sensitization. 

Wells has also shown that toxicity and sensi- 
tizing properties decrease equally by tryptic diges- 
tion, and that both disappear with the disappear- 
ance of heat coagulable proteins. According to 
Wells, the importance of the action of heat is due 
to the coagulation of protein, thus rendering it 
capable of being taken up and digested by the 
leucocytes. Casein and other proteins which do 
not coagulate on boiling suffer no change through 
heat until a temperature which destroys the pro- 
tein molecule is reached. 

That toxic and sensitizing substances may be 
closely related to the aromatic groups of the pro- 
tein molecule is suggested by the fact that gelatin 
which is devoid of tjTosin and contains little of 
other aromatic groups does not produce the phe- 
nomena of anaplrylaxis (Wells). 
Anaphylactic By the iniection of serum of sensitized animals 
it is possible to produce a passive sensitization, 
analogous to passive immunity, and in this way 
to demonstrate the presence of an anaphylactic 
antibody. This antibody has received the name of 
"anaphylactic (Eosenau and Anderson), or "al- 
lergin" (Anderson and Frost). It is possible to 
produce passive anaphylaxis in various animals, 
but, as in active anaphylaxis, the guinea-pig is 
best adapted to the purpose. Transmission of 
anaphylaxis from one species to, another is also 
possible. From rabbit to guinea-pig anaphylaxis 
is readily transmitted. 

The necessary interval of time elapsing between 
the injection of the serum containing anaphylactic 



Antibody. 



ANAPHYLACTIC ANTIBODY. 389 

antibody and the actual sensitization of the animal 
varies with the different methods of injection. In 
case of intraperitoneal injection this time is about 
twenty-four hours; in intravenous injections it is 
about one and one-half hours. 

Different means of measuring the sensitizing 
strength of antiserums have been suggested. Doerr 
and Buss injected decreasing quantities of the 
serum into guinea-pigs and then by injecting 
twenty-four hours later an intoxicating quantity 
of antigen into each of these pigs, the amount of 
antiserum necessary to produce sensitization was 
found. A second method is to inject a definite 
quantity of antiserum into each of a series of pigs 
and then twenty-four hours later to inject decreas- 
ing quantities of antigen to find the smallest 
amount necessary to cause acute death. Doerr 
and Buss suggest as a unit of anaphylaxis anti- 
serum or of anaphylactin such a serum as will in 
a dose of 1 c.c. intraperitoneally sensitize a 250 
gm. guinea-pig so that acute death may be pro- 
duced in twenty-four hours by injecting a sufficient 
quantity of antigen. 

The close connection between anaphylactogen Relation to 
and precipitinogen has already been alluded to. Antibodies. 
In a similar way, anaphylactin and precipitin are 
so closely allied that Friedberger, Doerr, and 
others consider them identical. As objections to 
this view it is pointed out that animals which do 
not readily produce precipitins, such as guinea- 
pigs and dogs, are most susceptible to sensitization; 
and secondly, that in the state of antianaphylaxis, 
to be described later, precipitins may be present, 
but apparently the anaphylactin is exhausted. 



390 INFECTION AND IMMUNITY. 

The anaphylactic antibody is thermostabile as 

are precipitins and agglutinins. That is, it resists 

a temperature of 56° C. for one-half hour. 

The Role of Michaelis and Fleischmann observed that dur- 

° m fn e AnS- ing and after anaphylactic shock the serum of the 

piiyiaxis. an i ma ] became p 00 r in complement. Sleeswijk 

found that following the second antigen injection, 

complement began to disappear after five minutes, 

and this disappearance became marked in thirty 

minutes. In cases in which death took place 

quickly and complement disappearance was not 

yet far advanced a further disappearance could be 

found by allowing the serum to stand for a while 

in the test tube. 

That the disappearance of complement is in 
itself not responsible for the anaphylactic shock 
is shown in two ways : first, the injection of com- 
plement before or after the second antigen injec- 
tion does not prevent shock, and secondly in most ' 
rapidly fatal shock, death takes place before com- 
plement has disappeared to any extent. Friedber- 
ger and Hartoch have also shown that injection of 
complement-binding salt solution inhibits ana- 
phylactic symptoms, when it is injected before the 
second injection of antigen (see Chapter on Com- 
plement Deviation). 
Anaphyio- In order to study further the relation of com- 
plement to anaphylaxis, Friedemann sensitized 
rabbits to ox-blood corpuscles and then added 
inactivated serum from these rabbits to ox erythro- 
cytes in the test-tube. He found that when com- 
plement was added to such a mixture, it became 
toxic and capable of producing anaphylactic symp- 
toms. By preventing complement binding, by 



toxin. 



THEORIES OF ANAPHYLAXIS. 391 

complementoid, etc., the formation of toxin was 
prevented. Friedberger was able in a similar way 
to produce substances which caused symptoms of 
anaphylaxis, by treating precipitinogens from 
various sources with precipitins in the presence 
of complement. He therefore supposes that this 
toxic substance, which he calls anaphylatoxin, is 
derived from the precipitate caused by precipitin 
acting on precipitinogen, and that it is the specific 
cause of intoxication in anaplrylaxis. As there 
exists a difference of opinion as to the identity of 
anaphylactic so there exist various theories as to 
the formation of anaphylatoxin. 

Eichet supposed that anaphylactic antibody and Theoretical 
antigen combined to form the poisonous substance tionV. era " 
which he called "apotoxin." Wolff-Eisner, Weieh- 
hardt, Friedemann and others consider anaphyl- 
actin to be of the nature of a lytic amboceptor, 
and that, by the action of complement through 
this amboceptor, a splitting of anaphylactogen 
into toxic substances takes place. Vaughan and 
Wheeler, with others, consider that in sensitiza- 
tion we have to do with the development of spe- 
cific proteolytic ferments which split the antigen 
into toxic groups similar in nature to their toxic 
products obtained by hydrolysis with alcohol and 
sodium hydrate. This view is supported by the 
fact that Biedl and Kraus have produced symp- 
toms of anaphylaxis by injection of split products 
of protein (Witte's peptone) in dogs. The pro- 
duction of increased protein splitting power of the 
serum after injection of foreign proteins as 
demonstrated by Abderhalden also supports the 
enzyme theory. According to these views, various 



392 



INFECTION AND IMMUNITY. 



Symptoms of 
Anaphylaxis. 



anaphylatoxins are of similar character but 
formed through the action of substances which 
are of specific nature. 

The symptoms of anaphylaxis vary with differ- 
ent animals. It is in the guinea-pig that most 
constant results are obtained. Symptoms begin 
at different intervals of time, after the second 
injection, with different proteins. With animal 
proteins, they appear in about fifteen minutes 
after intraperitoneal injection. The symptoms 
usually appear somewhat later with vegetable pro- 
teins. The animal becomes restless, there is a 
tendency to scratch, the hair stands on end, and 
difficulty in breathing comes on. Paralysis of the 
hind legs is common with animal proteins but is 
less common in plant proteins. The respiration 
becomes spasmodic, the animal is unable to stand, 
convulsive movements occur, and death follows 
rapidly when a fatal dose is given. When a non- 
lethal dose is given symptoms may be delayed for 
an hour. Death commonly occurs in fatal cases 
inside of an hour and often in less than half an 
hour. In intravenous and intracardiac injections, 
the symptoms follow much more rapidly than in 
intraperitoneal injections. In subcutaneous injec- 
tions, the symptoms occur long after injection and 
are inconstant and much less severe than with 
other ways of absorption. Fatal results are much 
more difficult to produce in subcutaneous injec- 
tions. 

The blood pressure is raised and lowering does 
not take place until shortly before death. A very 
important symptom is that described by Pfeiffer, 
who observed a constant sudden drop in tempera- 



MECHANISM OF SHOCK. 393 

ture. This symptom is considered of great diag- 
nostic value when the drop amounts to 2° or 3° C. 
and other experimental conditions are constant. 

In dogs, the symptoms vary greatly from those 
in guinea-pigs. Here a characteristic fall in blood 
pressure is found. Vomiting, involuntary urina- 
tion and defecation, paralysis and narcosis are 
common symptoms. 

The respiratory mechanism of shock in guinea- 
pig?, according to Auer and Lewis, is that of a 
spasmodic contraction of the unstriped muscle of 
the bronchioles resulting in obstruction of the 
lumen, acute emphysema and death from asphyxi- 
ation. 

Section of the vagi does not influence this pul- 
monary phenomena, indicating that the effect is 
a peripheral one. Schultz has shown that the 
unstriped muscle fiber of a sensitized guinea-pig 
contracts more vigorously when specific serum is 
applied directly to it than when other serum is 
used. Atropin, which acts on the- nerve endings, 
causes an inhibition of symptoms. Marked con- 
gestion of the abdominal blood vessels is a com- 
mon finding at autopsy. Various hypnotic and 
narcotic drugs have been described as inhibiting 
anaphylactic symptoms,' but the effect seems 
mainly due to a masking of symptoms. 

A sensitized animal which has recovered from a Antianaphyi- 
non-lethal toxic dose of protein is refractory to 
the action of a later close. The condition of such 
an animal is known as antianaphylaxis, and it 
has been demonstrated by failure to produce pas- 
sive anaphylaxis by using the serum of an animal 
in a state of antianaphylaxis, that the condition 



394 INFECTION AND IMMUNITY. 

is due to an exhaustion of anaphylactic antibody. 
In animals which have been actively sensitized, 
the period is a transient one, followed by a return 
of hypersusceptibility due to continued production 
of antibodies. In passively sensitized animals, as 
there is no further source of antibodies, the result 
depends on the amount of antigen injected. If, 
for instance, the animal is insufficiently sensitive 
to allow of death from a large toxic dose, the anti- 
gen remaining will produce an active sensitization. 
If the antigen is just enough to neutralize the 
anaphylactic the animal will then be, as before, 
sensitized. If the second dose is too small to 
neutralize the anaphylactic that which remains 
will be capable of producing further reactions. In 
animals immunized to proteins and which have a 
high concentration of antibodies in the blood, so 
that passive anaphylaxis may be transmitted to a 
second animal by the use of a small quantity of 
serum of the immune animal, a state of antiana- 
phylaxis may be produced by injections of amounts 
of antigen too small to produce a fatal result. 
In this case, we have an animal which is antiana- 
phylactic although possessing a serum containing 
a high concentration of anaphylactic Friedberger 
supposes that in this case the receptors of the cells 
are occupied by anaphylactic antibody which is 
not reached by the injected antigen, this being 
neutralized by the circulating anaphylactin. 
Tuberculin The relation of the tuberculin reaction to ana- 
ceptibiiity. phyiaxis (see Tuberculosis) has been the subject 
of much discussion. 

Yamanouchi succeeded in producing anaphyl- 
actic symptoms in guinea-pigs by sensitizing them 



SERUM DISEASE. 395 

with serum from tuberculous patients and then, 
twenty-four hours later, injecting tuberculin or 
tubercle bacillus emulsion. Bail passively sensi- 
tized guinea-pigs by the injection of tuberculous 
tissues and in this way obtained anaphylactic 
symptoms by injecting tuberculin after twenty- 
four hours. Helmholtz produced passive sensiti- 
zation against cutaneous reaction by the injection 
of serum from tuberculous guinea-pigs into nor- 
mal guinea-pigs so that after twenty-four hours, 
they gave a positive v. Pirquet test. 

In contrast to the results of Yamanouchi and 
Bail, other investigators have succeeded in passive 
sensitization of guinea-pigs by injection of serum 
from tuberculous animals either only occasionally 
or not at all. Production of anaphylaxis by active 
sensitization with tuberculin is possible only after 
repeated large doses. It would seem, therefore, 
that as in the case of other bacteria, typhoid, dys- 
entery, etc., the anaphylaxis is against the proteins 
of the tubercle bacillus rather than the toxin pro- 
duced by it. 

The untoward symptoms following the injec- 
tion of curative serums has been the subject of 
study by many investigators, particularly v. Pir- 
quet and Schick, Eosenau and Anderson, and 
Weaver. 

The reaction following a primary injection of 
serum appears after a period of time varying from 
a few minutes to several weeks. There may be 
slight redness and itching at the inoculation site, 
and swelling of the adjacent lymph glands. The 
prominent symptoms are fever, skin eruptions, 
edema and joint pains. Slight albuminuria and 
leukopenia have been noted. 



Serum Dis- 
ease. 



396 INFECTION AND IMMUNITY. 

The reaction varies in severity with the amount 
of serum used but individual variation and differ- 
ences in the serum are the most important factorSo 
The reaction following a second injection v. Pir- 
quet and Schick divide into (a) immediate, 
appearing after a few hours, or (b) delayed, 
appearing after a few days or a week. The symp- 
toms are similar to those following a primary 
injection but are more likely to be severe and may 
be accompanied by vomiting, convulsions, collapse 
and, rarely, death. 

The abnormal reactions following a second 
injection are more likely to appear when the 
patient has had a reaction after the primary injec- 
tion ; secondly, when large amounts of serum have 
been given in the primary injection; and thirdly, 
with a history of asthma (especially in asthma in 
which the attacks are brought on by proximity to 
horses) or hay fever. 

It has been suggested that, in cases necessitating 
second injections of antitoxin, a small amount, 
1 c.c. or less, be given as a test dose to be followed 
by the necessary therapeutic dose twenty-four 
hours later. 

It is important to be sure that the antitoxin is 
not injected into the vein because of the fact that 
anaphylactic symptoms are produced as much 
more readily by intravenous injections. This can 
be avoided by preliminary aspiration just before 
injection to see that blood does not enter the 
syringe. 

Eosenau and Anderson have demonstrated the 
presence of anaplrylactin in the blood of men who 
have been injected with antitoxic horse serum. 



SERUM DISEASE. 397 

It has been suggested that by passive sensitiza- 
tion of guinea-pigs with patient's serum, we can 
ascertain whether or not there is any danger in 
second injections of serum. 

It has also been suggested that a cutaneous test, 
similar to a v. Pirquet tuberculin test, be made 
with horse serum to find out whether or not hyper- 
susceptibility to horse serum be present. 






PART THREE-SPECIAL. 



CHAPTEE XXIV. 



Although a consistent classification of the infec- 
tious diseases, on the basis of immunity, is impos- 
sible at the present time, a certain grouping is de- 
sirable for the sake of convenience. The following 
arrangement of those diseases we are able to con- 
sider is made on a basis which is partly etiologic, 
partly with reference to the pathogenic properties 
of the micro-organisms, and partly to the nature 
of the reactions excited in the body by infection or 
immunization. In some instances nothing more 
than general analogies suggest themselves as a 
basis for the grouping, which is necessarily provi- 
sional and imperfect. 

GROUP 1. 

Diseases, natural or experimental, which are 
caused by soluble toxins of bacterial, animal or 
plant origin. Infection or immunization induces 
immunity to subsequent attacks (except in hay fe- 
ver), the immunity being characterized by the 
formation of serum antitoxins, and occasionally of 
bacteriolysins and agglutinins. The serums of 
highly immunized animals are protective and cur- 
ative for the corresponding intoxications in man 
and other animals. 

A. BACTERIAL DISEASES. 
I. DIPHTHERIA. 

Bacillus diphtheria, or the Klebs-Loeffler bacil- 
lus, was discovered by Klebs in 1883, and more 



DIPHTHERIA BACILLUS. 399 

fully described by Loeffler in 1884. It answers all 
Koch's laws in its relationship to the disease of 
diphtheria. It is a non-motile, rod-shaped organ- ciiaracter- 
ism having about the length of the tubercle bacil- oKSmSm?" 
lus, but twice its thickness. One end commonly 
presents a flask-like enlargement. It stains by 
Gram's method, with the ordinary anilin dyes, anO 
with the special stain of Neisser shows a peculiar 
granulation, the granules of Babes-Ernst. It is 
readily cultivated, especially on solid media which 
contain serum and in various bouillons. It tends 
to grow in coherent masses and under the micro- 
scope the cells often show a characteristic phalanx- 
like arrangement. 

The diphtheria bacillus is an obligate parasite 
having no vegetative existence outside of the body, 
is very resistant to desiccation and may remain 
virulent in a dried state for from one to five 
months. Its life in water varies from a few days 
to several weeks, having its shortest existence in 
distilled water and its longest in hydrant water 
which has been boiled. It disappears more quickly ■ 
from unboiled hydrant water. It is very suscepti- 
ble to ordinary antiseptics, being killed in a few 
minutes by corrosive sublimate even in a dilution 
of 1 to 10,000. 

The sources of infection may be enumerated as Methods of 
follows : 1. From the false membranes, sputum 
or excretions of the mouth, pharynx, nose, con- 
junctiva and deeper respiratory passages of in- 
fected individuals. 2. From convalescents and 
those who have fully recovered, even after serum 
treatment. Virulent organisms may persist in the 
pharynx or nose of convalescents for weeks and 
months, as in one of Prip's cases in which they 



400 INFECTION AND IMMUNITY. 

were found twenty-two months after recovery. 3. 
From the upper air passages of healthy persons 
who may never have had diphtheria, but who have 
been in direct or indirect contact with the dis- 
eased. Kober obtained virulent bacilli from 8 per 
cent, of the individuals who had been in direct 
contact with patients, and he states that 0.83 per 
cent, of the people at large carry with them viru- 
lent organisms. This condition may well account 
for the "spontaneous" origin of diphtheria in the 
susceptible. 4. From cases of latent diphtheria as 
represented by chronic pharyngeal diphtheria and 
chronic rhinitis fibrinosa. 

Hence, infection takes place chiefly by direct 
contact, but frequently also by indirect contact. 
Transmission by kissing or by other means of inti- 
mate contact, by using infected cups or toys, is 
well recognized. "Droplet infection," i. e., from 
infected globules of mucus or saliva which the pa- 
tient emits when speaking or coughing, may occur, 
„ but perhaps is not of great significance. The same 
probably is true of "dust infection," although, as 
stated, the organism may remain living and viru- 
lent in a dried state for a long time. The disease 
is rarely transmitted from animals to man, al- 
though such transmission may occur from the cat, 
which occasionally suffers from true diphtheria. 
The diphtheria of fowls is due to another organ- 
ism. 

The upper air passages, more rarely the conjunc- 
tiva, wounds and the vulva, are recognized as in- 
fection atria. 
pathogenesis. ^he local and general phenomena of diphtheria 
are caused by the soluble toxin which the organ- 
ism secretes. Although the toxin is not absorbed 



DIPHTHERIA BACILLUS. 401 

through, nor does it injure the unbroken skin, it 
produces necrosis of the mucous surfaces and un- 
derlying tissue at the site of infection. Through 
the wounded surface fibrin-forming elements es- 
cape, as a consequence of which successive layers 
of fibrin are deposited and the fibrin, together with 
the necrotic surface, leucocytes and associated 
micro-organisms constitute the membrane which 
so often marks the disease clinically. The local 
process is similar in diphtheria of cutaneous 
wounds. The toxin becomes generalized by absorp- 
tion through the lymphatic circulation. 

Characteristically the bacilli are confined to the Localization 
site of infection. Although diphtheritic bacterie- of the Bacilli - 
mia rarely occurs, the bacilli have been found oc- 
casionally in the blood and viscera of fatal cases. 

The clinical and anatomic conditions lead us to 
believe that the parenchymatous organs, the lym- 
phatic tissues and the cells of the nervous system 
contain receptors with which the toxin unites, in- 
asmuch as these tissues suffer demonstrable injury 
during the disease. When the toxin is injected 
subcutaneously into animals, localized edema and 
necrosis occur; hence, the connective tissues may 
also take up a portion of the toxin, diverting it, so 
to say, from the more vital organs. 

Mixed infections render diphtheria a more dan- Mixed 
gerous disease. According to Baumgarten, the I,lfectlons - 
streptococcus is associated with the diphtheria ba- 
cillus in most cases of diphtheria. The observa- 
tion of Eoux and Yersin that the streptococcus in- 
creases the virulence of the diphtheria bacillus 
both in the test-tube and in animal experiments 
may explain to some degree the severity of the dis- 
ease when accompanied by streptococcus infection. 



402 INFECTION AND IMMUNITY. 

Aside from the local influence of the streptococcus, 
however, a general invasion by this organism may 
occur, with such consequences as acute nephritis 
or lobular pneumonia, and in this condition the 
diphtheritic infection may fall into the back- 
ground in importance (septic diphtheria). Post- 
diphtheritic suppurations commonly are caused by 
the pyogenic cocci, but sometimes in association 
with the diphtheria bacillus itself. Rarely the 
bacillus is found in pure culture in lobular pneu- 
monia, a condition which Flexner and Anderson 
produced experimentally in animals. In puer- 
peral infections with the streptococcus a puerperal 
diphtheria is sometimes superimposed. 
immunity and Very young children resist diphtheritic infec- 
susceptibiiity. ^ Qm ^ certain degree of immunity may be trans- 
mitted by the mother. Observations on animals 
show that when the blood and milk of the mother 
contain antitoxin, the offspring acquires some pro- 
tection, which, however, may disappear after the 
cessation of nursing. Polano claims that anti- 
toxin passes from the mother to the child through 
the placenta. From the second to the seventh or 
eighth year children usually are very susceptible. 
This susceptibility is not uniform, however, for 
many children escape infection, whereas others, 
under the same conditions, contract the disease. 
Following this period susceptibility decreases and 
after the fifteenth year the disease is relatively 
rare. 

The cause of the immunity which develops in 
the absence of a preceding infection has not been 
sufficiently investigated. In some cases consid- 
erable amounts of antitoxin are found in the 
serum, perhaps enough to account for the immun- 



IMMUNITY IN DIPHTHERIA. 403 

ity. The prolonged presence of bacilli of low 
virulence in the nose or pharynx, or mild attacks 
of the disease which have not been recognized, 
may cause the development of antitoxin. As 
stated in an earlier chapter, the loss of suitable 
receptors may be a factor in this type of acquired 
immunity. 

Hypertrophic tonsils and chronic pharyngitis 
appear to be predisposing causes in children. 

Spontaneous recovery (active immunity) is due Active im- 
to the formation of the specific antitoxin by munlty - 
the tissues of the patient. We may regard the 
relationship of the leucocytes to diphtheritic in- 
fection as not definitely settled. Although leuco- 
cytosis is a fairly constant occurrence and may go 
as high as 25,000 to 30,000 to the cubic milli- 
meter, it is difficult to dissociate that due to the 
diphtheritic infection from that caused by a mixed 
infection with the streptococcus. Both polynu- 
clears and mononuclears are increased, the latter 
being especially marked in children (Ewing). 
The opsonin content of the serum in diphtheria is 
below normal at the onset of the disease. As the 
symptoms subside and the membrane disappears, 
the opsonic index rises considerably, returning to 
normal in from two to nine days. 

Injection of dead diphtheria bacilli in suitable 
numbers into rabbits is followed by a rise in the 
opsonic index. Injection of dead diphtheria bacilli 
may prove of service in ridding the throats of 
bacillus-carriers of bacilli (Tunnicliff). 

Eecent experiments have substantiated the ideas 
of Behring that bacteriolysins are of little impor- 
tance in immunity in diphtheria. 



404 INFECTION AND IMMUNITY. 

The duration of active immunity to diphtheria 
varies greatly. Usually an individual has diph- 
theria but once, yet not infrequently those are en- 
countered who suffer from repeated attacks. In 
some instances the susceptibility continues into 
adult life. 

Propiiyiaxis. The advent of serotherapy justifies no relaxa- 
tion in the customary prophylactic measures, such 
as isolation of the diseased, quarantine and disin- 
fection. A patient should not be considered harm- 
less until his mouth, phar}mx and nose are free 
from bacilli, a condition which may be brought 
about by antiseptic applications, and for the de- 
termination of which repeated bacteriologic exam- 
inations are necessary. The danger that others 
who have been in contact with the patient may 
carry the infection should be met by appropriate 
treatment. It is not to be forgotten that anti- 
toxin does not destroy the organisms. The injec- 
tion of antitoxin is our most effective measure for 
individual prophylaxis. 

serotherapy. Experimentally, it is possible to vaccinate 
against diphtheria by the inoculation of dead diph- 
theria bacilli, or extracts of agar cultures (Lip- 
stein, also Bandi and Gagnoni), but the conditions 
hardly warrant the use of this method for pro- 
tecting man. Extracts of the organisms may be 
mixed with antitoxin and injected for protection. 
This is the so-called serovaccination. 

The efficacy of diphtheria antitoxin is so well 
known that little comment is needed. It has 
caused a reduction of more than 50 per cent, in 
the mortality of the disease; from 41 per cent, to 
8 or 9 per cent., according to Baginsky. 



DIPHTHERIA ANTITOXIN. 405 

For prophylaxis from 500 to 1,000 units are 
generally recommended, although some foreign 
authorities give only 250 units. Karely, individ- 
uals who have received such treatment develop 
diphtheria within twenty-four hours after the in- 
jection. In these cases it is probable that infec- 
tion has already occurred and symptoms appear 
before the antitoxin is thoroughly distributed. 
Naturally one may contract diphtheria after the 
antitoxin is eliminated. 

For curative purposes the amount actually re- 
quired depends on the virulence of the infection 
and the duration of the disease. Inasmuch as the 
virulence may not be known accurately, what ap- 
pears to be an excess of antitoxin is always de- 
manded. Having in mind the average dose of 
3,000 units recommended by the recent edition of 
the United States Pharmacopeia, the physician 
must be guided by the conditions in the individ- 
ual case. Less than 2,000 units are rarely indi- 
cated, and as many as 10,000 and 14,000 units 
may be given without detriment to the patient. 
There should be no hesitation about repeating a 
dose within twenty-four hours in the absence of 
distinct improvement. 

Eansom and Knorr state that if the antitoxin 
is given intravenously, which may be done without 
danger, the action of the serum is about eight 
hours earlier than when given subcutaneously. In 
severe and in late cases it is advisable to use this 
method of introduction, the serum first being 
warmed to the temperature of the body. It should 
be remembered, however, that the dangers of ana- 
phylactic symptoms are much increased by intra- 
venous injection. 



Paralysis. 



406 INFECTION AND IMMUNITY. 

It is probable that few cases are so mild or so 
hopeless, unless moribund, that the omission of 
antitoxin is justifiable. 
Diphtheritic The belief that antitoxin favors the development 
of diphtheritic paralysis is no longer held. If 
there has been an actual increase in the percentage 
of cases which suffer from paralysis, as sometimes 
stated, it is because a larger number of severe 
cases is saved; and the severe cases are those 
in which the patients most frequently develop 
paralysis. If we accept the view of Ehrlich that 
a special toxin of weak affinity for the anti- 
toxin, i. e., the toxon, causes the paralysis, we find 
all the more justification for large doses of 
antitoxin, for antitoxin neutralizes the toxon as 
well as the toxin. On the basis of experi- 
mental work Eansom concludes: "Transferring 
the results (of experiments) to practice among 
human beings, we may expect liberal doses of 
antitoxin given early in the illness to influence 
favorably the subsequent paralysis; and this fa- 
vorable influence is likely to manifest itself, not so 
much in the local paralyses (soft palate, etc.), as 
in such fatal symptoms as failure of the heart. 
Severe cases, however, are likely to be followed by 
some paralysis in spite of even large doses of anti- 
toxin." 

Cases in which there is severe mixed infection, 
septic diphtheria, respond less favorably to anti- 
toxic therapy than uncomplicated cases. At some 
time a mixed serum therapy suited to the mixed 
infection may be possible. 

The suggestion made by Wasserman of a com- 
bined treatment with bactericidal and antitoxic 
serums has not been applied practically. 



PSEUDODIPHTHERIA BACILLUS. 407 

Inasmuch as the serum of the patient does not Agglutination 
develop agglutinins, the agglutination test is of 
no value for the recognition of the disease. If ani- 
mals are immunized with the bacillus, agglutinins 
are said to be formed. The serum of such an ani- 
mal may be used for the identification of a culture 
made from the throat, but this would have no 
practical value, for the diagnosis may be estab- 
lished by the ordinary bacteriologic methods much 
more quickly and satisfactorily. It is difficult to 
obtain a homogeneous suspension of the bacillus 
for the agglutination test. 

Microscopically and culturally the bacillus of Psendodipn- 
diphtheria can be distinguished with difficulty Bacnii. 
from a variety of other organisms which belong to 
the same group, and which are called pseudodiph- 
theria bacilli. The latter are frequently found in 
diphtheritic throats, but occur also in the upper 
air passages and conjunctiva in the absence of all 
lesions. On the whole, they are non-pathogenic, 
but occasionally a culture is found which causes a 
subcutaneous infiltration at the point of injection 
in an experimental animal. Hamilton cultivated 
one which was distinctly virulent for animals. Their 
pathogenicity, however, is altogether different 
from that of the diphtheria bacillus inasmuch as 
diphtheria antitoxin does not protect against them 
nor do animals which are immunized with pseudo- 
diphtheria bacilli become immune to the toxin of 
diphtheria. The Bacillus xerosis, which is thought 
by some to be the cause of xerosis conjunctivae, 
but which is also found under normal conditions, 
is a pseudodiphtheria bacillus. The animal experi- 
ment is the only positive means of differentiating 
the true from the pseudodiphtheria bacilli. Some 



408 



INFECTION AND IMMUNITY. 



consider them as diphtheria bacilli which have lost 
their virulence. 

The presence of these organisms may complicate 
the diagnosis of diphtheria in some cases, but 
there is little danger of serious error. If one 
found organisms resembling the bacillus of diph- 
theria in a membranous sore throat which was ac- 
companied by severe symptoms, there could be no 
wavering in the decision to use antitoxin. 



Character- 
istics of the 

Microorgan- 
ism. 



II. TETANUS. 

In 1884 Carle and Eattone demonstrated the 
infectiousness of tetanus by inoculating the pus 
from an infected wound into rabbits; 11 of the 12 
inoculated rabbits died of tetanus. In 1885 the 
bacillus was discovered by Nieolaier, and Kitasato 
cultivated it artificially in 1889. 

The organism is rather long and slender (2 to 
4 microns long, 0.3 to 0.5 broad), possesses many 
flagella and has a small amount of motility. It 
stains readily with the ordinary anilin dyes and by 
Gram's method. In young cultures isolated cells 
and threads predominate, but after a few days 
spore formation begins; eventually all the adult 
cells degenerate and the culture consists entirely 
of spores. The spores have a larger diameter than 
the bacillus, are situated at one end of the cell and 
give the latter the characteristic "drumstick" 
form. The organism is a strict anaerobe and is 
obtained in pure culture with some difficulty. 
Morphologically it is difficult to distinguish from 
the bacilli of malignant edema and symptomatic 
anthrax. 

Few organisms are distributed more widely and 
generously than the bacillus of tetanus. It is most 



TETANUS BACILLUS. 409 

abundant in street dirt and in tilled ground which 
has been fertilized with manure. Mcolaier found 
it in twelve out of eighteen samples of earth. It 
is less abundant in timber land. Such a distribu- 
tion is easily accounted for, since the bacillus 
seems normally to be an inhabitant of the intesti- 
nal tract of the horse, cow and sheep, and is often 
found in that of man and other animals. It oc- 
curs on dirty clothing and readily gains access to 
dwellings with dust in which it may be blown and 
carried about. Tetanus frequently develops in 
gunshot wounds in which dirty clothing is carried 
into the tissue, and several instances of house 
tetanus have been noted in which a number of in- 
dividuals in the same dwelling have contracted the 
disease following injury. Particular localities may 
be heavily infected. In certain tropical districts a 
large percentage of new-born infants die of tetanus 
neonatorum, and puerperal tetanus has prevailed 
alarmingly in Bombay. It has been suggested 
that the custom of bleaching the linen on the 
ground may be responsible for the prevalence of 
the disease in these localities, but from the fact 
that it has decreased under aseptic practices the 
general lack of surgical precautions is probably of 
greater importance. Tetanus has resulted from 
the injection of impure gelatin for hemostatic 
purposes. The bacillus has been found in sea 
water. 

The ability of the bacillus to proliferate outside 
the animal body has not been determined. Some 
observers hold that it exists as a vegetative organ- 
ism only in the intestinal tract of animals, but the 
possibility of proliferation in soil is by no means 
excluded, particularly since it is so often found in 



410 INFECTION AND IMMUNITY. 

association with organisms which are known to 
favor its growth. When incrusted in solid ma- 
terial and accompanied by suitable saprophytes it 
may readily find the anaerobic conditions which 
are demanded for germination of the spores. 
Resistance. The spores are very resistant. In one instance 
they remained virulent for eleven years on a splin- 
ter of wood. They may be killed in six days by 
direct sunlight. In comparison with non-spore- 
forming organisms they are very resistant to anti- 
septics. Kitasato found that they were killed in 
five minutes by steam, in fifteen hours by a 5 per 
cent, carbolic acid, in two hours by 5 per cent, 
carbolic acid to which 0.5 per cent, of hydro- 
chloric acid was added, in three hours by 1 to 1000 
corrosive sublimate and in thirty minutes by the 
same solution to which 0.5 per cent, hydrochloric 
acid had been added. 
infection Tetanus is conspicuously a wound infection and 
dition^wnich that it develops so frequently from wounds which 
infection 1 ! are contaminated with earth is readily understood 
from the distribution of the organisms as cited 
above. Considering, however, the great number of 
such wounds and the prevalence of the bacillus, 
the rarity of the disease is remarkable. In expla- 
nation of this fact investigations have shown that 
the organism is not a vigorous parasite, that it 
demands special conditions for its development in 
the tissues. According to Vaillard and Rouget, 
the spores when washed free of toxin do not cause 
tetanus, but rather are taken up and destroyed by 
leucocytes. 
Anaerobic The bacillus, furthermore, is a strict anaerobe, 
■w<mnd" demanding for its development a wound from 
which the air is largely excluded. It is well known 




CONDITIONS OF INFECTION. 411 

that penetrating wounds in which infected ma- 
terial is carried beneath the fasciae, as the rusty 
nail wounds, also those accompanied by deep lac- 
erations, as wounds inflicted with blank cartridges, 
or those in which dirt and micro-organisms have 
been ground into the tissues, as in crushing inju- 
ries, are prone to be followed by tetanus. Under 
such conditions the bacillus lies deeply imbedded 
in the tissues and remote from the air. 

Of equal importance is the presence of foreign inhibition of 
matter and particularly of other micro-organisms. 
Relatively superficial wounds in which there is 
laceration of the tissue with consequent necrosis, 
as in wounds by toy pistols, even the paper-cap 
pistol, are well adapted for the development of 
tetanus if the germs were on the skin at the time 
of injury. Necrotic tissue favors the proliferation 
of the tetanus bacilli in two ways. In the first 
place it seals up the wound to a certain extent, 
and thus provides the requisite anaerobic condi- 
tion; in the second place it would seem to prevent 
phagocytosis of the bacilli in some obscure way. 
It has been suggested that the strong, chemotactic 
relation which exists between necrotic material 
and leucocytes causes the latter to take up the dead 
tissue rather than the bacilli. That innocent for- 
eign material may favor the development of teta- 
nus in the presence of the microbes was shown by 
Vaillard and Rouget: tetanus would develop in 
the presence of an artificially produced hematoma 
or a subcutaneous fracture while in the absence of 
such predisposing factors the bacilli were taken up 
by phagocytes. 

Saprophytic organisms and the pus-producing J"f e e c * ions 
cocci which are usually found in wounds contami- 



INFECTION AND IMMUNITY. 



Pex'iod of 
Incubation. 



nated with earth appear to favor the development 
of tetanus. This may be explained to some extent 
by their ability to increase the virulence of the 
tetanus bacillus, a condition which is noted in cul- 
tures. In the wound they may engage the leuco- 
cytes in phagocytosis and prevent ingestion of the 
tetanus bacilli. As aerobic organisms they may 
facilitate development of the bacilli by consuming 
local oxygen. 

Our great harvest of tetanus following Fourth- 
of-July injuries is closely associated in the first 
place with the warm, dry season in which the 
bacilli are more readily disseminated with dust, 
and in the second place with the nature of the 
wound and mixed infections, as described above. 

Occasionally tetanus follows the simplest 
wounds, which may have healed entirely before 
symptoms develop. In "idiopathic tetanus" and 
in the so-called "tetanus rheumaticus," which fol- 
lows exposure to cold, the infection atria are un- 
known. In the latter instance a latent infection, 
whicn is stirred into activity by the reduction of 
resistance which often follows exposure, may be 
present; avirulent tetanus bacilli (?) were culti- 
vated from the lungs of one such patient. The oc- 
casional occurrence of tetanus following diphthe- 
ria and typhoid suggests that infection may take 
place through wounds of mucous surfaces. Neither 
the bacillus nor its toxins penetrate the unbroken 
skin or mucous membranes, and the alimentary 
tract is further protected by the ability of the gas- 
tric and pancreatic juices to digest the toxin. 

The incubation period varies from two or three 
days to several weeks. In the statistics of Eose 20 
per cent, of the cases showed symptoms in the first 



ACTION OF TETANUS TOXIN. 413 

week, 45 per cent, in the second, and about 30 per 
cent, in the third or fourth weeks. The shorter 
the incubation period the more fatal the disease. 
In the statistics cited the mortality with short in- 
cubation was 91 per cent.; when the incubation 
period was moderate it was 81.3 per cent., and 
when prolonged, 52.9 per cent. The nearer the 
infection atrium is to the central nervous system 
the shorter is the incubation period; fr head teta- 
nus" develops quickly. 

The pathogenic properties of the tetanus bacil- 
lus reside in its soluble toxins, of which two, teta- 
nospasmin and tetanolysin, are known. The char- 
acteristic nervous phenomena of the infection de- 
pend on the action of the former, whereas the lat- 
ter, a hemolytic toxin, is of minor importance. As 
in diphtheria, a systemic distribution of the bacilli 
is not necessary for the development of the dis- 
ease, the toxin being produced by the organisms in 
the wound, whence it is carried to the nervous 
tissue by way of the lymphatics. Particularly in 
mixed infections tetanus bacilli may be carried to 
neighboring lymphatic glands and eventually 
reach the circulation; pure cultures have been ob- 
tained from the heart's blood in experimental 
work. The blood, on account of its content in 
oxygen, is thought to be unfavorable for the 
growth of the organism. 

Just before death the toxin has been demon- 
strated in the blood of man by injecting some of 
the serum into mice. Its excretion in the urine is 
questionable. Tetanus produces no characteristic 
anatomic changes, although degenerative lesions 
in the ganglionic cells occur. Death usually occurs 
from asphyxia caused by contractions of the dia- 



min. 



414 INFECTION AND IMMUNITY. 

phragm, or muscles of the glottis, or from cardiac 
failure. In some instances the blood has been 
found more or less laked because of the action of 
the tetanolysin. 
Tetanospas- Tetanus toxin (tetanospasmin) has a very 
strong affinity for the nervous tissue of susceptible 
animals. This may be demonstrated in test-tube 
experiments in which the toxin is mixed with an 
emulsion of the nervous tissue; the nervous tissue 
neutralizes the toxin more or less completely, as 
determined by subsequent inoculations of the mix- 
ture (Wassermann's experiment). It is held by 
certain authorities that the toxin attacks only the 
nervous tissue in man; in some of the lower ani- 
mals, however, various organs, especially the liver, 
have an affinity for the toxin. 

The method by which tetanus toxin reaches the 
central nervous system has been the subject of 
much speculation and experimentation. Eecent 
observations by Marie and Morax and by Ransom 
and Meyer show with a great degree of probabil- 
ity that it is absorbed by the end organs of the 
motor nerves and from there passes to the gang- 
lionic cells through the axis cylinders. This ab- 
sorption takes place very quickly; when the toxin 
is given intravenously it disappears from the blood 
in the course of minutes. It has been found in the 
nerves within an hour and a half after subcutane- 
ous injection. Its further transmission centrally 
occupies more time and, indeed, the investigators 
mentioned explain the rather long incubation 
period of the disease on the basis of the time re- 
quired for this transmission. The brief incuba- 
tion period in "head tetanus," accordingly, would 



IMMUNITY IN TETANUS. 415 

depend on the short distance the toxin is obliged 
to travel to reach the ganglionic cells. 

Although the toxin appears not to be taken up 
by the sensory nerves, a painful form of the dis- 
ease, tetanus dolorosa (Meyer), may be pro- 
duced experimentally by injecting the toxin into 
the posterior roots of the spinal nerves. Eoux 
caused "cerebral tetanus" by introducing the toxin 
into the cerebral tissue; the condition is charac- 
terized by absence of contractures. "Local teta- S^^JSSJ^ 
nus," in which the muscles in the vicinity of infec- 
tion or inoculation are involved in contractures, is 
the first symptom of tetanus in experiment ani- 
mals; it rarely occurs in man except in head teta- 
nus. The phenomenon depends on the fact that 
the toxin, being transmitted through the motor 
nerves, reaches first the ganglionic cells which cor- 
respond to the infected area. 

According to Metchnikoff, the only natural im- 
munity which man possesses to tetanus is leuco- 
cytic and this may be sufficient to protect under 
favorable conditions. The observations of Vaillard 
and Eouget (cited above) support this claim. Sus- Tets»ns. s 
ceptibility depends not only on the presence of 
suitable receptors in the nervous tissue, but also 
on the degree of affinity which exists between 
these receptors and the toxin. In man and some 
animals this affinity is very great, whereas in fowls 
it is weak and an enormous amount of toxin is re- 
quired to cause tetanus. A further proof of this 
weak affinity in non-susceptible animals rests in 
the fact that the toxin when injected into the blood 
remains unabsorbed for a long time, whereas in 
susceptible animals it disappears very quickly. Ac- 



INFECTION AND IMMUNITY. 



quired immunity depends on the presence of anti- 
toxin in the circulation. 
Prophylactic Tetanus antitoxin is a thorough prophylactic. 
Antitoxin. This fact has been heralded so extensively in re- 
cent years that there can be little excuse for ignor- 
ance on the part of any physician. At the same 
time, the returns from the "Fourth" show that the 
principle is not yet deeply imbedded in the medical 
mind. It is quite certain that a large percentage 
of these fatalities could be prevented by two injec- 
tions of antitetanic serum, one at the time of in- 
jury and a second from five to eight days later. 
An epidemic of puerperal tetanus in an obstetric 
ward in Prague was checked by prophylactic injec- 
tions of the antitoxin. In a certain section of 
France 4,000 horses, with injuries commonly fol- 
lowed by tetanus, received antitoxin and none de- 
veloped the disease. 

No degree of efficacy on the part of the anti- 
toxin, however, justifies disregard of the surgical 
care which the wound demands. From the facts 
cited it is clear that thorough and frequent disin- 
fection of the wound, free drainage, the removal 
of all foreign and necrotic material, and the ac- 
cess of air are measures of eminent importance. 
Punctured wounds should be opened up. Anti- 
toxin, preferably as a powder, may be used in the 
wound, and the serum infiltrated into the adjacent 
tissue. 

The principles which apparently underly the ill 
success of the antitoxin as a curative agent were 
treated of in Chapter XXII, Part II. Its adminis- 
tration as early as possible after symptoms have 
appeared is demanded. After symptoms have ex- 
isted for more than thirty hours Behring main- 



Cnrative 

Value of 

Antitoxin. 



VALUE OF ANTITOXIN. 417 

tains that there is no hope of cure by the subcuta- 
neous route. Inasmuch as forty hours or more are 
required for complete absorption from the subcuta- 
neous tissue, intravascular injection of at least the 
first dose would seem to be indicated. Yet by 
neither of these methods is the most essential end 
accomplished, for the antitoxin does not reach the 
nerves nor can it be recognized in the cerebrospinal 
fluid in conspicuous quantities. The most that 
such injections accomplish is the neutralization of 
the circulating toxin, that which is not yet on its 
way to the central nervous system through the mo- 
tor nerves. It is, of course, important to neutral- 
ize the circulating toxin and it must be done quick- 
ly, for in the course of a few hours the fatal quan- 
tity of toxin may have been absorbed; "a dose of 
antitoxin which would save in the morning may 
be without effect in the evening." 

At the same time it is of greater immediate im- Method of 
portance to neutralize that which has already en- jSStoxfi?. 
tered the peripheral nerves, and if possible to tear 
away some of the toxin already bound by the gang- 
lionic cells. To acomplish this object, or to at- 
tempt it, special procedures are demanded. We 
may then consider the antitoxic treatment as fol- 
lows: 

First: The neutralization of the toxin which 
has already been absorbed by the peripheral nerves 
and spinal cord at a point as near the vital centers 
as possible. This involves surgical exposure of the 
large nerves of the part as near the trunk as possi- 
ble and their infiltration with antitoxin (Kansom 
and Meyer), and in desperate cases the infiltra- 
tion of the antitoxin in the spinal cord in the 
ricinity of the medullary centers. From five to 



418 INFECTION AND . IMMUNITY. 

fifteen minims may be injected into the nerve 
trunks at a sitting, and the operation may be re- 
peated on subsequent days; the needle should be 
partially withdrawn and reinserted in different di- 
rections during the injection. Eogers recommends 
tying loose ligatures around the nerves after the 
operation so that they may be readily drawn up 
and identified for further injections. In order to 
reach the medulla the intracerebral method of 
Roux or that of Eogers may be utilized. Kocher 
has devised a technic for the intracerebral injec- 
tions. Anterior to the parieto-frontal suture and 
to one side of the median line the scalp is pre- 
pared, and a hole drilled through the skin and 
skull, having its direction toward the foramen 
magnum. By means of a long needle, the ventri- 
cle is penetrated and the serum, after injection, 
finds its way to the fourth ventricle to the imper- 
iled respiratory and cardiac centers; 10 c.c. may 
be injected. Eogers seeks to accomplish the same 
end by a different technic. He introduces the 
needle between the sixth and seventh cervical ver- 
tebrae, punctures the cord deeply, and injects from 
20 to 30 minims at a sitting. Although there is 
danger of intraspinal hemorrhage in the proce- 
dure, no ill effects were noted. It has been recom- 
mended also that the cerebrospinal fluid be with- 
drawn by means of lumbar puncture and substi- 
tuted by antitoxin. Some physicians who have 
used this method report favorable results. 

Second: The neutralization of all toxin which 
is not yet bound by the nervous tissue or absorbed 
by the motor nerves. This demands the infiltra- 
tion of the wound and surrounding tissue with the 
antitoxin, and injection of a sufficient amount of 



DOSAGE OF TETANUS ANTITOXIN. 419 

the serum into the circulation in order that circu- 
lating toxin may be neutralized. The intraneural, 
intraspinal or intracerebral injections should al- 
ways be supplemented by subcutaneous or intra- 
vascular injections. The first dose should be given 
intravenously, whereas subsequent injections may 
be given subcutaneously. The injections should 
always be repeated. 

According to Anderson, the prophylactic dose 
of tetanus antitoxin standardized according to the 
official standard adopted by the United States 
Public Health and Marine-Hospital Service is 
1,500 units. As a curative it should be given in 
doses of from 3,000 to 20,000 units, repeated dur- 
ing the course of the disease. 

Agglutination has no practical significance for 
diagnostic purposes. An agglutinating power has 
been noted in the serum on the eighth day. Ag- 
glutinins may be produced by immunizing animals 
(rabbits) either with the bacilli or the toxin. Id 
the latter case the formation of the agglutinin is> 
due to the presence of agglutinogenic receptors in 
the toxin solution. 

III. BOTULISM. 

Botulism is a peculiar form of meat poisoning 
in which the nervous system is involved princi- 
pally. From twenty-four to thirty-six hours after 
the poisonous meat is eaten salivation, ptosis, dila- 
tation of the pupils and paralysis of the ocular 
muscles develop and death from bulbar paralysis 
occurs rapidly in from 25 to 30 per cent, of the 
cases. In the event of recovery, convalescence may 
extend over weeks or months. 



Bacillus 
Botulinum 



420 



INFECTION AND IMMUNITY. 



Infected 
Meats. 



The disease occurs especially in some European 
districts in which improperly preserved or raw 
meats are eaten. The term "ichthyosisnms" , is 
applied to a similar or identical disease which is 
caused in Eussia by salted fish. In 1895 von 
Ermengem investigated a ham which had caused 
50 cases of botulism, and isolated from it an anae- 
robic, spore-forming bacillus, which produces a 
soluble toxin capable of causing the entire symp- 
tom-complex of the disease. 1 The organism pos- 
sesses flagellar has limited motility, grows only in 
alkaline media, and in contrast to most pathogenic 
organisms prefers a relatively low temperature 
(18-25° C). It is probably on account of its 
physiologic activity at such temperatures that it 
is able to produce its toxin in meats which have 
been kept in a cool place. It is found in decom- 
posed ham and various sausages (Leberwurst and 
Blutwurst), and probably gains access to the meat 
after the animal has been killed. Von Ermen- 
gem investigated two hams from the same animal. 
One was under anaerobic conditions being covered 
with brine, while the other was exposed to air; 
only the former was toxic. The organisms may be 
absent from the superficial portion of the meat, 
but abundant in the deep portion. The spores are 
relatively susceptible to heat, being destroyed by 
a temperature of 80° C. for one hour. Aside from 
its occurrence in meat, nothing is known of the life 
history of the bacillus. 

The disease is caused by the toxin which has al- 
ready been produced in the meat and not by the 

1. Other pathogenic organisms, especially B. enteritidis 
and B. coli communis, and recently the paratyphoid bacil- 
lus, have been found in poisonous meats. The term 
botulism formerly was applied to various forms of meat 
poisoning. 



BOTULISM TOXIN. 421 

activity of the organism after it has reached the 
alimentary tract (v. Ermengem). If an extract 
of the meat is made with water and the bacteria 
removed from the latter by nitration, the fluid 
shows characteristic toxicity for animals. This 
experiment may be nsed for determining the pres- 
ence of botulism toxin in suspected meat. The 
guinea-pig is the most susceptible animal. 

According to v. Ermengem, the bacillus does not 
proliferate in the body, nor does it produce toxin 
vigorously at body temperature; hence, he consid- 
ers it to be a strict saprophyte — a pathogenic sap- 
rophyte. 

The toxin is taken up by the circulation from 
the alimentary tract and is not destroyed by the 
gastric and pancreatic juices, differing in this re- 
spect from the toxins of diphtheria and tetanus. 
It is prepared artificially by growing the organism 
anaerobically in suitable bouillon and subsequently 
sterilizing the fluid by nitration. Like the other 
soluble bacterial toxins, it is susceptible to the ac- 
tion of air and light, and is destroyed by a tem- 
perature of from 60 to 70° C. 

That the toxin has a special affinity for the nerv- 
ous tissues is evident from the symptoms of the 
disease; histologically, the ganglionic cells show 
degeneration in fatal cases. Further evidence of a 
strong affinity between the toxin and nervous tissue 
lies in the ability of the latter to neutralize the 
toxin in the test-glass. The toxin, however, ap- 
pears not to be so selective in its action on the 
nervous tissue as the toxin of tetanus, for in bot- 
ulism degenerations of the glandular organs, and 
of the vascular endothelium with consequent hem- 
orrhages are characteristic anatomic findings. 



Pathogenesis 



422 INFECTION AND IMMUNITY. 

Man appears to be very susceptible to the intoxica- 
tion, whereas dogs, rats, and cats are relatively im- 
mune. The toxin is pathogenic by subcutaneous or 
intravascular injection. 

According to v. Ermengem, the bacilli when in- 
oculated subcutaneously do not proliferate, but are 
taken up by the phagocytes immediately or after 
they have been carried to other organs. Animals 
which have recovered from infection or which have 
been immunized acquire rather strong immunity 
to subsequent inoculations, the immunity being 
antitoxic. 
Prophylaxis The proplrylactic measures consist in the avoid- 
and toxin" ance of poorly preserved and improperly cooked 
meats, especially sausages. Botulism would seem 
to be very rare in this country where raw meats 
are not used extensively. 

The antitoxin (Kempner) has proved of some 
value in animal experiments, but its commercial 
preparation has not been warranted on account of 
the rarity of the disease. 

IV. BACILLUS PYOCYANEUS. 

pathogenic For a long time it was thought that the "bacillus 
of blue pus" was of no importance as an infectious 
agent for man, although its pathogenicity for ani- 
mals had been recognized experimentally. It is 
found with some frequency in the blood and or- 
gans of man at autopsy, when death has resulted 
from some other infection or chronic disease, and 
in such instances it is supposed that a so-called 
"agonal invasion" by the organism has occurred. 
During recent years, however, several cases of pri- 
mary pyocyaneus septicemia have been observed, 
the bacillus having been obtained from the blood 



Properties. 



BACILLUS PYOCYANEUS. 423 

in pure cultures during life or from the blood and 
organs shortly after death. It has been found as 
the sole organism in meningitis and vegetative en- 
docarditis. Some of the cases indicate, however, 
that a previous lowering of resistance, as that 
caused by tuberculosis and syphilis, is important 
for general invasion by the bacillus. It has been 
found several times in suppurative processes in the 
middle ear, and would seem to be either the cause 
or a strong adjuvant in some cases of severe enter- 
itis, especially in childern. In systemic infec- 
tions, the symptoms are typhoidal in character, 
with high temperature, diarrhea and a tendency 
to the formation of hemorrhages in the skin and 
internal organs. 

The Bacillus pyocyaneus is widely distributed its Manifold 
and that it causes so few infections is probably due 
to its low pathogenic power. It is an organism of 
manifold activities. It produces a substance, pyo- 
cyanin, which, when exposed to the air, assumes a 
bluish tint, and on which the color of the pus de- 
pends; pyocyanin is soluble in chloroform, from 
which it may be precipitated in crystalline form. 
Under proper conditions the organism also forms 
a fluorescent pigment. It produces a strong pep- Ferments. 
tonizing ferment, coagulates milk, and in old 
cultures an autolytic ferment is found which di- 
gests many of the bacilli. As stated in a previous 
chapter, Emmerich and Lowe have identified a 
bacteriolytic ferment, pyocyanase, which dissolves 
the anthrax bacillus and other organisms. The 
ferment nature of this substance is in some doubt, 
inasmuch as it resists the boiling temperature. 
Dietrich thinks its action is due to the production 
of osmotic changes. Old cultures contain a liemo- 



424 



INFECTION AND IMMUNITY. 



Toxin and 
Antitoxin. 



Antitoxic and 

Bactericidal 

Serums. 



lytic agent (pyocyanolysin) of an alkaline nature, 
which resists boiling and is not a true toxin, since 
immunization with it does not yield an antitoxin 
(Jordan). In addition to the products mentioned, 
the organism secretes a true soluble toxin for 
which it is possible to obtain an antitoxin, and 
possesses, furthermore, an endotoxin for which 
an antitoxin can not be obtained. 

The soluble toxin of Bacillus pyocy emeus is not 
produced in large amounts. It differs from the 
other soluble toxins in its resistance to heat, with- 
standing a temperature of 100° C. for five min- 
utes. It produces the symptoms which are char- 
acteristic of infection with the living organism, 
the principal anatomic changes being parenchyma- 
tous degenerations and ecchymoses, the latter sup- 
posedly being due to degenerative changes in the 
endothelium of the vessels. 

By immunizing with young cultures grown on 
an agar surface, a serum which is bactericidal 
and opsonic is obtained. On the other hand, 
if an older toxin-containing bouillon culture be 
used, the serum is opsonic, bactericidal and 
antitoxic. The serum which is bactericidal and 
opsonic has no power of neutralizing the toxin. 
The toxin solution contains not only the true 
toxin, but also quantities of endotoxin which 
were Hberated as the dead bacilli were dissolved. 
Inasmuch as the antitoxin neutralizes only the 
true toxin, leaving the endotoxin unbound, the 
toxicity of the filtrate cannot be destroyed entirely 
by antitoxin, a condition which is brought out 
clearly when the attempt is made to neutral- 
ize a multiple of the simple fatal dose by the 
corresponding amount of antitoxin. In such mul- 



OTHER TOXINS. 425 

tiples a fatal amount of endotoxin is present. 
Although a strong antitoxin may be obtained, it 
would appear to be of little practical importance 
because of the rarity of infections by the bacillus. 

Infection in man has caused the formation of Aggiutina- 
agglutinin in several instances, but it has been tlon# 
absent in others. An agglutinating serum is read- 
ily produced by artificial immunization. 

V. OTHER SOLUBLE BACTERIAL TOXINS. 

Soluble toxins, of perhaps secondary impor- 
tance, which are produced by the staphylococcus 
and streptococcus, will be considered in the sections 
dealing with these organisms. It seems probable 
that they do not represent the essential toxic 
agents of the cocci, but rather that the toxicity of 
the latter depends chiefly on the action of endo- 
toxins. 

B. INTOXICATION BY SOLUBLE PLANT TOXINS. 
I. HAY FEVER. 

Dunbar separated from the pollen of various 
grains a toxin which is able to precipitate typical 
attacks of hay fever in those who are susceptible, . 
having first demonstrated that the crude pollens 
cause the disease. The pollen from the following 
are said to contain the toxin : Eye, barley, wheat, 
maize (corn), dog's tail, couch-grass, millet, rice 
and some others. The so-called autumn-catarrh 
which is common in America may be due to a 
slightly different toxin coming from the golden- 
rod, rag-weed, and perhaps other autumnal flower- 
ing grains. 

The toxin usually is associated with certain The Toxin. 
starch-like granules which are contained in the 



426 INFECTION AND IMMUNITY. 

pollen, but it occurs also in pollens which do not 
contain these granules. It may be extracted with 
water or salt solution, is precipitated by alcohol, 
resists the boiling temperature, and is of an al- 
buminous nature. 

When the crude pollen reaches the conjunctiva, 
Pathogenesis, nasal or bronchial mucous membranes of suscep- 
tible individuals, the toxin is dissolved out by the 
secretions and absorbed by the lymphatics. When 
applied to the conjunctiva it causes swelling, red- 
ness and lachrymation. It is carried by the tears 
to the nose and here causes excessive secretion, 
swelling of the mucous membrane and sneezing. 
It may become distributed systemically as a result 
of absorption from the free surfaces and cause the 
asthmatic attacks and general symptoms which are 
seen in the intoxication. When injected subcuta- 
neously into the arm both the asthmatic attacks 
and coryza-like symptoms were produced. 
Ant serum Dunbar's antitoxic serum (pollantin) is ob- 
(Poiiantin). tained by immunizing horses with the toxin. It 
seems to be of undoubted value in a certain per- 
centage of cases, but fails unaccountably at times. 
It is, perhaps, most effective when used in the 
prodromal stage, the attacks being thereby pre- 
vented. Its failure in certain instances may be 
due in part to the inefficacy of the antitoxin 
against the toxins of certain pollens. Again, in 
certain individuals the affinity of the toxin for 
the tissues may be unusually great so that a more 
vigorous use of the remedy is demanded. 

Liibbart and Prausnitz published statistics of 
285 cases, of which 65 were autumnal. In ordi- 
nary hay-fever the serum gave positive results in 
57 per cent., partially positive in 32 per cent, and 



POLL AX T IX. 427 

negative results in 11 per cent, of the cases. In 
autumnal catarrh, 70 per cent, were positive, 19 
per cent, partially positive, and 11 per cent, nega- 
tive. 

The small bottles of antitoxin are accompanied 
by a pipette with which from one to several drops 
may be instilled into the eye or the nose. 

The serum does not cure permanently and one 
who is susceptible should carry a vial for imme- 
diate use during the hay-fever season. Eepeated 
use of this serum has been observed to result in 
sensitization of the patient to horse serum. Dun- 
bar recommends in these cases that a very dilute 
solution be used. 

Inhalations of increasing amounts of pollen, 
beginning with very minute quantities, has also 
been tried with the idea of active immunization. 

It is probable that further study of hay fever 
as a phenomenon of anaphylaxis will result in the 
explanation of points concerning the disease which 
are not yet clear. 

II. OTHER PLANT TOXINS. 

Eicin, from the seeds of Ricinus communis; 
abrin, from Abrus precatorkis; crotin from the 
seeds of Croton tiglium; and robin, from the leaves 
and bark of the locust tree (Robinia pseudoacacia) 
are chiefly of experimental interest. They are 
similar in their action, are very toxic to animals, 
producing both local and general changes with 
fatal termination when given in sufficient doses; 
they have pronounced agglutinating action on the 
erythrocytes of most animals, and in some in- 
stances are slightly hemolytic. By guarded im- 
munization antitoxins may be obtained for them. 



428 



INFECTION AND IMMUNITY. 



Kobert gave the name of pliallin to a toxic sub- 
stance which may be extracted from poisonous 
mushrooms, particularly the "Deadly Amanite" 
{Amanita phalloides). In some countries many 
deaths are caused by eating this variety: Kussia, 
Germany, Italy, France, Japan (Ford). Phallin 
is very toxic for animals and is strongly hemolytic 
for many bloods. By immunization Ford has re- 
cently obtained an antitoxin which neutralizes the 
hemolytic action of the poison, and which in a dose 
of 0.5 c.c. protects rabbits against five fatal doses 
of the toxin. The toxin is an aqueous extract of 
the dried plants. 

C. INTOXICATION BY SOLUBLE ANIMAL TOXINS. 
I. POISONING BY SNAKE BITES. 

The poison apparatus of snakes consists of 
a secretory gland on each side which communi- 
cates with a tubular fang by means of a duct. In 
the passive state the fangs are directed backward 
on the roof of the mouth, but when the animal 
strikes their points are made to project forward 
and the poison is forced through the canals by 
muscular compression of the sac. The venom is 
a glandular secretion. The colubridinse, among 
which is the American coral snake, possess im- 
movable fangs. 

The venoms of different snakes vary a great 
deal in their toxic properties. The most impor- 
tant constituents are those which attack the nerv- 
ous system (neurotoxin), the blood corpuscles 
(hemolysins and hemagglutinins) and the endo- 
thelium of the blood vessels, causing hemorrhages 
(hemorrhagin, an endotheliotoxin). The three are 
independent. 



SNAKE VENOM. 429 

The neurotoxin causes death by paralysis of the 
cardiac and respiratory centers. The hemolysin 
appears to be of less importance as a cause of 
death. 

The venoms of the cobra, water-moccasin, da- variations 
boia and some poisonous sea-snakes are -essentially properties 
neurotoxic, although they have strong dissolving f^Sngf* " 
powers for the erythrocytes of some animals. In 
studying the hemolytic powers of the venoms of 
cobra, copperhead and rattlesnake, Flexner and 
Noguchi found cobra venom to be the most hemo- 
lytic and that of the rattlesnake the least. They 
attribute the toxicity of rattlesnake poison chiefly 
to the action of hemorrhagin. The same authors 
studied the action of different venoms on the cells 
of various animals and by absorption experiments 
found independent cytotoxins for the testis, liver, 
kidney and blood. Not only was there a distinct 
cytotoxin for each organ of an animal, but also 
for the same organ of different animals, results 
which speak for a remarkable complexity of 
venom. Certain venoms contain a leucocytic 
toxin. 

That venoms contain proteolytic ferments is Ferments. 
shown by their ability to digest gelatin and fibrin. 
This power may be related to the softening of the 
muscles which has been noted clinically in cases of 
poisoning. The rapid decomposition of the body 
which follows death by snake-poisoning is asso- 
ciated with a decrease in the bactericidal power of 
the blood, which," according to Flexner and No- 
guchi depends on fixation of the complement by 
the venom. 

The hemolysin and neurotoxin, and perhaps 
other cytolysins of venom, consist of amboceptors 



430 INFECTION AND IMMUNITY. 

Amboceptors which in themselves are non-toxic; they become 
ment. toxic only through the aid of complements which 
are present in the body of the poisoned animal. 
In this instance, complement which usually is a 
source of protection becomes a source of danger to 
the animal possessing it. Not only does ordinary 
serum-complement serve for activation, but Kyea 
discovered that cells (erythrocytes) may contain 
another kind of complement, an "endocomple- 
ment," which activates the amboceptors after the 
latter have combined with the cells. Flexner and 
Noguchi found that this also was the case with 
the neurotoxic amboceptors. 

The ability of lecithin to activate the hemolytic 
amboceptors of cobra venom and the preparation 
of cobra-lecithid (Kyes) were described in Part II, 
Chapter XVI. In the preparation of cobra-leci- 
thid the neurotoxin is separated from the hemo- 
lysin, the former remaining in solution, whereas 
the latter settles as a precipitate in combination 
with the lecithin. Immunization with the neuro- 
toxin isolated in this way causes the formation 
of a specific antineurotoxin (Elliot). The neuro- 
toxin may also be abstracted from the venom by 
treating the latter with the nervous tissue of a 
susceptible animal (Flexner and Noguchi). 

The hemolysin is distinct from the hemagglu- 
tinin and the latter may be eliminated by heating 
the venom to from 75° to 80° C. In the action of 
venom on erythrocytes agglutination precedes he- 
molysis. 

Toxoids and The toxins may be converted into toxoids by 
heat or treatment with chemicals. Immunization 
with toxoids causes the formation of antitoxins. 



SNAKE ^ ENOM. 431 

Radium is said to destroy the toxicity of venom 
(Physalix). 

The antivenin of Calmette is obtained by im- 
munizing horses with a mixture of venoms (80 
per cent, cobra, 20 per cent, viper ine venom) which 
are attenuated before injection. Six months are 
required to produce a strong serum. The claim 
of Calmette that his serum is effective against all 
snake-venoms is erroneous. It neutralizes those 
venoms the toxicity of which depends largely on 
neurotoxins and hemolysins, but has little influ- 
ence on rattlesnake poison, the essential toxin of 
which is hemorrhagin. Antivenin for the rattle- 
snake and water-moccasin may be prepared by im- 
munization with the corresponding venoms which 
have been attenuated by weak acids. Noguchi has 
produced serum of such strength that it promises 
to be of practical value in the treatment of rattle- 
snake bites. 

As indicated previously, the action of venom is 
preceded by no appreciable incubation period ; 
hence, an antitoxin to be effective must be admin- 
istered not later than a few hours after the bite 
has occurred. Noguchi found in relation to anti- 
venin for the rattlesnake that the quantity of anti- 
toxin necessary to save was quadrupled three hours 
after intravenous injection of two fatal doses of 
venom. Fortunately the venom is less toxic when 
introduced subeutaneously. 

II. OTHER ZOOTOXINS. 

Phrynolysin, which is present in the blood and 
skin of certain toads, has been studied especially 
by Proscher. It is a thermolabile, hemolytic toxin 



432 



INFECTION AND IMMUNITY. 



for which an antitoxin can be obtained by immuni- 
zation. 

Arachnolysin, obtained from the bodies of cer- 
tain spiders, is a hemolytic toxin, which by immun- 
ization yields a specific antitoxin. 

A poison, with properties resembling those of 
snake venom, may be obtained from the caudal 
segment of the scorpion. Antitoxin is produced 
by immunization. 

Ichthyotoxin, a name given to the toxic proper- 
ties of eel serum, is composed of a neurotoxic and 
a hemotoxic constituent. 

From the poisonous glands of certain fish 
(Trachinus draco) a highly toxic, thermolabile 
substance is obtainable, for which an antitoxin can 
be prepared by the immunization of rabbits 



CHAPTEE XXV. 
GKOUP II. 



Acute infectious diseases caused by bacteria 
which do not secrete strong soluble toxins in cul- 
ture media, but which contain endotoxins (toxic 
protoplasm). Infection or immunization causes 
immunity of considerable or prolonged duration. 
In active immunity the serums agglutinate the 
corresponding organisms and are protective for 
other animals 1 (anti-infectious), but have little or 
no curative power. The formation of antitoxins 
is not definitely established. In most instances 
vaccination has been accomplished. Clinically 
there is leucocytosis in some instances and hypo- 
leucocytosis in others (typhoid and Malta fever). 

A. The serum in acquired immunity is increased 
in bactericidal and opsonic power. 

I. TYPHOID FEVER. 

Eberth first saw Bacillus typhosus in micro- 
scopic preparations of the mesenteric lymph glands 
and spleen of a typhoid patient, in 1880. Koch 
also observed it at about the same time, and 
stained it in the intestinal wall, spleen, liver and 
kidney. It was obtained in pure culture by Gaffky 
in 1884. 

The organism is rod-shaped, 0.5 to 0.8. by from 
1 to 3 microns in dimensions, with nothing char- 
acteristic in its morphology. It possesses from ten 

1. This has not been established in regard to Malta fever. 



434 INFECTION AND IMMUNITY. 

to twelve flagella situated at the ends and on the 
sides and is actively motile under suitable condi- 
tions. It forms no spores and is readily cultivated 
on many media. 

The bacillus is one of the rather numerous "in- 
testinal group" of organisms, certain members of 
which are so similar that they can be differentiated 
only by means of special cultures, animal experi- 
ments, or the agglutinating, opsonic and bacteri- 
cidal action of specific immune serums. 2 
Distribution The organism has been cultivated from earth 
Bacillus, and infected water, and from the feces, urine, 
blood, rose-spots and the various organs of typhoid 
patients. In many instances in which an epidemic 
has certainly been caused by an infected water sup- 
ply attempts to cultivate the bacillus from the 
water have failed. The organisms may not have 
been included in the samples which were analyzed, 
or, what is equally probable in certain instances, 
they have died out in the water by the time the 
disease was so widespread as to be considered epi- 
demic. Its occurrence in Nature depends on the 
distribution of the excretions of the patients and 
carriers. The viability and virulence of the bacil- 
viaMiity his in water, earth, etc., vary with the nature of 
Resistance, its surroundings. It has been found to live 
for periods of from 2 to 4 weeks to 2 or 3 
months in water, from 3 to 4 months in milk, 
from 3 to 5 months in surface water, and from 
11 to 16 months in sterilized earth; 100 days 
in ice, from 12 to 30 days in oysters, from 50 to 

2. Of this group the bacilli of dysentery, paratyphoid 
bacillus, Bacillus enteritidis of Gartner, colon bacillus and 
Bacillus alcaligenes, in addition to the typhoid bacillus, are 
the most important because of their similar morphologic and 
cultural properties and the pa thogenicity of certain of them. 






BACILLUS TYPHOSUS. 435 

80 days when dried on clothing, and for 3 months 
in typhoid feces. When in water or moist earth 
which contain many saprophytes its life is short- 
ened. It survives drying for many months, al- 
though direct sunlight kills in the course of a few 
hours. 

That the typhoid bacillus secretes a soluble Endotoxin. 
toxin, has not been satisfactorily demonstrated. It 
contains, however, an endotoxin which may be 
obtained in solution by the autolytic digestion of 
cultures, by extracting ground-up bacilli or by 
squeezing out the plasma under high pressure. Up 
to the present time, immunization with none of 
these preparations has resulted in the production 
of an antitoxic serum of accepted value. 

Typhoid fever may become epidemic either Typhoid 
through a contaminated water and food supply or 
by contact infection. When due to infected water 
there is something characteristic about the explo- 
sive-like suddenness with which dozens or even hun- 
dreds are stricken within a short period. The water 
of streams, small lakes or reservoirs may become 
infected from an ill-constructed out-house, or from 
discharges which have been thrown on the ground 
in their vicinity. Typhoid stools thrown on the 
ground adjacent to wells have caused small epi- 
demics. Fruit, vegetables and milk cans may be 
infected by washing them with contaminated water, 
and it is supposed that the disease may be acquired 
from oysters which have lain in water contami- 
nated with sewage. 

The importance of the so-called bacillus-carriers 
as a source of epidemics of typhoid has been 
recently emphasized by a great many observers. 



436 INFECTION AND IMMUNITY. 

Park estimates that from 2 to 5 per cent, of all 
people who recover from typhoid, continue to 
excrete typhoid bacilli by way of the urinary or 
alimentary tracts. Park also estimates that one 
out of every 500 adults who have never had 
typhoid, harbor typhoid bacilli. The bile is gen- 
erally regarded as the medium in which the bacilli 
perpetuate themselves in the case of the carriers. 

By whatever means an apidemic is set in motion 
primarily, it is usually aggravated and prolonged 
by the occurrence of contact infections (indirect 
contact). The hands of the nurse, physician, or 
others who come in contact with the patient be- 
come contaminated from the stools, urine, soiled 
linen or skin of the patient, and the organisms 
subsequently are transferred to food, drinking 
water, or in other accidental ways reach the mouth. 
Each new case is a fresh focus from which infec- 
tion may be carried to others, and the chances of 
milk and food infection become greater as the 
cases multiply. When the discharges are not dis- 
infected or are improperly disposed of, soil or 
house infection may occur and the possibility 
of transmission by germ-laden dust becomes of 
importance. Dust infection from dried urine 
or feces and drop infection from urine, water, 
or the sputum of the patient are theoretical- 
ly possible, but would seem to be of minor sig- 
nificance. That flies may carry the organisms 
from open vaults or cesspools and deposit them on 
food or in drinking water has been appreciated 
in epidemics in military camps and elsewhere. 
Typhoid bacilli have been cultivated from flies 
which were taken from the vicinity of infected 
material. 



INFECTION ATRIUM. 437 

The bacilli gain access to the body through The infer- 
tile lymphoid tissue of the intestinal tract (Pey- 
er's patches and the solitary follicles). The occur- 
rence of primary infection of the lungs through 
inhalation of infected dust is possible, but has 
not been definitely proved. In this instance typhoid 
bacillemia might occur either with or without 
intestinal infection. In the latter case it would 
seem essential that some local lesion exist in 
the lungs or elsewhere from which organisms 
could constantly be supplied to the blood Neufeld 
doubts the ability of the typhoid bacillus to pro- 
liferate in the blood, because of the strong bacteri- 
cidal poAver of the latter, and considers that infec- 
tion takes place through the intestines even in cases 
of "typhoid without intestinal lesions." 

The incubation period is subject to considerable incubation 

1 d . Period. 

variations. In a series of cases in which the date 
of exposure was known, 62 per cent, showed, symp- 
toms in from 20 to 25 days, 2 per cent, in from 14 
to 20 days, and 2 per cent, later than 30 days. 

Quickly following the development of intestinal Localization 
lesions, the bacilli reach the circulation by way Baciiu. 
of the lymphatics, and through the action of the 
bactericidal constituents of the blood (amboceptor- 
complement complex and possibly leucocytes) they 
are killed and dissolved in large quantities. It 
is now generally believed that only through the 
disintegration of the bacterial cells are their toxic 
constituents thrown into solution in the body, a 
condition which is necessary in order that the tis- 
sues be injured. Infection of the blood stream 
with living organisms, in the early stages of the 
disease and preceding relapses, occurs in probably 
all the cases. 



438 INFECTION AND IMMUNITY. 

Diagnosis It is possible to establish the diagnosis of 
cui?«?e* typhoid fever by cultivating the bacilli from the 
blood, even before the serum has developed suffi- 
cient agglutinating power to cause agglutination. 
A small flask of bouillon is inoculated with from 
1 to 5 c.c. of blood, drawn from the median vein 
of the arm, and after twenty-four hours of incu- 
bation a small portion of it is plated out. Colonies 
which develop on the plates may be identified by 
the usual bacteriologic methods, or the agglutina- 
tion test may be performed with a known anti- 
typhoid serum. After from the tenth to the four- 
teenth day the organisms can rarely be cultivated 
from the blood; the bactericidal substances and 
phagocytic power of the blood may have so 
increased by this time that circulating bacilli are 
killed rapidly. 

In from one-fourth to one-third of the cases, in 
the third week, or during convalescence, the bacilli 
appear in large numbers in the urine, in which 
they may persist for many weeks. According to 
Kanjajeff, they are discharged into the urine from 
metastatic foci in the kidneys. 

Many of the symptoms, complications and se- 
quela? of typhoid fever, as the rose-spots, enlarged 
spleen, bone lesions, and in some instances nervous 
lesions and pneumonia, depend on the distribution 
of the bacilli. This is in contrast to the conditions 
in diphtheria and tetanus, in which the distribu- 
tion of the bacilli is of little significance for the 
involvement of particular organs. The anatomic 
changes and clinical symptoms suggest that the 
lymphoid tissue and central nervous system have 
a special affinity for the toxic constituents of the 
typhoid bacilli. 



CHANGES IN INTESTINAL LYMPH NODES. 439 
The greatest changes take place in the organs Endothelial 



(lymphoid) which contain the bacilli most con- 
stantly and in the greatest numbers. It is here 
that the toxic substance may be present in greatest 
concentration, as a consequence of the continual 
solution of the organisms. Mallory describes an 
enormous hyperplasia of the endothelial cells, es- 
pecially those of the lymphatic structures. The 
cells are phagocytic, and especially in the lymphoid 
tissue of the intestines and in the mesenteric 
lymph glands, englobe and destroy the lymphoid 
cells on a large scale. It seems probable that the 
endothelial proliferation which has been described 
is due to the rather mild but prolonged action of 
the dissolved toxic constituents of the typhoid ba- 
cillus; the condition is that of an inflammatory 
hyperplasia. It has been suggested that the hypo- 
leucocytosis of typhoid fever is due to the destruc- 
tion of the lymphocytes in the lymphoid organs by 
the endothelial phagocytes. 

The granular and fatty degenerations of the 
parenchymatous organs do not differ from those 
seen in many acute infections. 

The conditions in the intestinal tract would 
seem to favor mixed infections, especially by the 
colon bacillus and streptococcus, and the primary 
infection probably decreases the resistance to sec- 
ondary invasion. The role of the colon bacillus in 
typhoid fever is perhaps not definitely established, 
although it has been found in the circulation, in 
abscesses, and in the urine in cases of cystitis ac- 
companying the disease. The typhoid and colon 
bacilli grow well together. A mixed general in- 
fection with the streptococcus causes a grave sep- 
tic condition characterized by an irregular tem- 



Hyperplasia. 



Infections. 



440 INFECTION AND IMMUNITY. 

perature curve. This condition may be discovered 
by blood cultures. It is thought that the strepto- 
coccus does not increase the toxicity of the typhoid 
bacillus, the result being rather a summation of 
the intoxication of the two infections. Post- 
typhoidal suppurations are often due to the strep- 
tococcus and in many of the metastatic complica- 
tions (parotitis, pleurisy, peritonitis, meningitis, 
otitis media) streptococci and staphylococci have 
been found. Pneumococcus pneumonia not infre- 
quently complicates typhoid fever. A combined 
infection of typhoid and malaria is said to occur in 
the tropics; the complication is grave. Typhoid 
and diphtheria may occur together, and typhoid 
may be superimposed on acute tuberculosis. 
immunity The period of greatest susceptibility to typhoid 
and Slt P y ; is found from the fifteenth to the twenty-fifth 
years. The resistance of infants and children is 
not satisfactorily explained. A certain amount of 
resistance inherited from the mother may persist 
for some years after birth. It is known that anti- 
bodies may pass from the mother to the fetus 
through the placenta. In very early life the tissues 
may respond more energetically to incipient in- 
fection by the rapid formation of typhoid anti- 
bodies, or the phagocytic cells may be more active. 
The conditions which render older people less sus- 
ceptible are no better understood. A loss of suit- 
able receptors may have occurred so that the toxic 
constituents of the bacilli find no anchorage in the 
body, or the affinity between the receptors and the 
toxic constituents may have become less. The in- 
dividual during the course of years may have been 
gradually immunized by the entrance of non- 
pathogenic quantities of the bacilli into the cir- 



IMMUNITY TO TYPHOID 441 

dilation. That resistance to typhoid infection is 
decreased by low nutrition and overwork is a long- 
known fact. 

A large amount of protection is afforded by the Natural and 
hydrochloric acid of the gastric juice, and it is immunity. 
reasonable to believe that suppression or an insuf- 
ficient amount of hydrochloric acid may favor the 
passage of living bacilli to the intestines. Normal 
human serum is rather strongly bactericidal for 
the typhoid bacillus, and the leucocytes ingest and 
destroy it. Metchnikoff ascribes natural immun- 
ity to the action of the microphages. 

The immunity which follows an attack of Duration of 
typhoid fever is generally of long duration, but immunity. 
second attacks occur with some frequency. Accord- 
ing to Dreschf eld's figures 0.7 per cent, of individ- 
uals are affected twice. It has been noted that 
limited communities which have experienced an 
epidemic may remain relatively free from the dis- 
ease over a period of some years, although neigh- 
boring districts are attacked. All the susceptible 
persons having had the disease, a state of temporary 
immunity is created. 

Acquired immunity is characterized by an in- 
crease of the bactericidal amboceptors, opsonins, 
agglutinins and typhoid precipitins in the serum. 
It has been shown that recovery is accompanied by 
an increase in concentration of antibodies. Bac- 
tericidal amboceptors reach a concentration two or 
three times that of normal serum and then return 
gradually to normal, reaching a normal concentra- 
tion in a few months. Opsonins increase in con- 
centration as do bactericidal amboceptors, but 
remain high for many months. Stone believes that 
this increased power of phagocytosis constitutes 



442 INFECTION AND IMMUNITY. 

the most important factor in the immunity result- 
ing from an attack. 

This is not clear from the clinical standpoint 
because of the hypoleucocytosis which is some- 
what characteristic of typhoid — a hypoleucocytosis 
caused chiefly by a disappearance of the micro- 
phages. It has been suggested that our con- 
clusions as to hypoleucocytosis are based on ex- 
amination of the peripheral blood, whereas the 
mesenteric vessels may show hyperleucocytosis. 
Mallory, however, found a striking absence of 
microphages even in the intestinal vessels. Con- 
cerning a theory that the hyperplasia of the lym- 
phoid organs serves as a substitute for the hyper- 
leucocytosis, we may recall the findings of Mallory 
that this hyperplasia is chiefly one of endothelial 
cells. The importance of these endothelial cells 
for the destruction of typhoid bacilli needs further 
investigation. 
prophylaxis. Prophylaxis should begin with the thorough 
disinfection of the stools and urine of typhoid pa- 
tients, and this should be continued until they no 
longer contain typhoid bacilli. It is not good 
hygiene to discharge a patient until bacteriologic 
examination of stools and urine show them to be 
free from the organisms. It would be difficult to 
carry out this rigid precaution under all condi- 
tions, but at all events the stools and urine may be 
disinfected for a reasonable period, say through- 
out convalescence. There is no sufficient reason 
for the neglect of the bacteriologic examination in 
hospital practice. There is a growing sentiment 
that typhoid patients in hospitals should be iso- 
lated in wards or rooms in which there is a fixed 
routine for the disposal of infectious materials — 






enamin. 



THERAPY. 443 

urine, stools and sputum. Soiled linen, the bath 
water of typhoid patients, the remnants of food 
and drink, and the eating utensils should be dis- 
infected before removal from the room. Nurses 
or attendants should not eat or drink in typhoid 
rooms. 

Hexamethylenamin may be of value in causing Hexametiiyi 
the disappearance of bacilli from the urine, and 
the advisability of using the drug as a routine 
measure for public safety is worthy of con- 
sideration. The room should be kept free from 
flies and eventually it should be disinfected, pref- 
erably by formalin. During an epidemic, in case 
the water supply of a community is susceptible to 
contamination, all water used for drinking, wash- 
ing of vegetables and eating utensils, should be 
boiled, and that used for general cleaning may be 
otherwise disinfected. The possibility of dust in- 
fection of a house should not be disregarded. 

The typhoid carrier remains one of the difficult 
problems of prophylaxis. That carriers may be 
rid of bacilli by inoculation with dead bacilli, has 
not been satisfactorily demonstrated except in 
some instances. Systematic detection and treat- 
ment of these carriers is hard to carry out. 

There are two methods of specific prophylaxis serotherapy 
against typhoid: 1, the injection of antityphoid ?ion. Vaccina 
immune serum; 2, preventive inoculation with 
killed cultures of the bacilli. Antityphoid serum 
confers a fairly strong and immediate immunity 
which, however, is of short duration, because of 
the rapid elimination of the serum. Its use as a 
general preventive, therefore, is not advocated. 

Wright has been influential in showing the util- Wright's 
ity of protective inoculations against typhoid. His Results. 






444 INFECTION AND IMMUNITY. 

first experimental work was published in 1896. 
Since that time the inoculations have been carried 
on extensively in Bristish regiments in India and 
South Africa. The occurrence of typhoid among 
the inoculated was one-half that among the unin- 
oculated, and the inoculations reduced the mor- 
tality of the disease by one-half. The protection, 
so far as known, lasts for two or more years, al- 
though in some instances infection has occurred in 
The vaccine. f r0 m three to six months after vaccination. 

The methods of preparation of the vaccine are 
elaborate in order to insure sterility and standard- 
ization. Cultures of the bacillus are grown in 
bouillon for from twenty-four to forty-eight 
hours, and then sterilized at 60 C. The contents 
of several flasks are mixed in order to obtain a 
uniform distribution of organisms, and standard- 
ization is then accomplished by estimating the 
number of bacilli in a cubic centimeter of the vac- 
cine. The purity is insured by bacteriologic tests, 
and for preservation phenol or liquor cresolis com- 
positus is added. 

Wright has abandoned his original method of 
giving a single injection and now recommends two 
moderate doses, which are given from eight to 
fourteen days apart. The first dose includes a 
quantity of vaccine which contains from 750,000,- 
000 to 1,000,000,000 of bacilli, the second 1,500,- 
000,000 to 2,000,000,000. Wright finds that "the 
inoculation of these quanta induces an ample 
. elaboration of antibodies without producing any 
severe constitutional reaction." The inoculations 
increase the bactericidal, opsonic and agglutinating 
powers of the serum and it is concluded that an 
increased resistance to typhoid intoxication is 






THERAPY. 445 

established because the second injection causes 
milder symptoms than the first. The phagocytic 
power of the leucocytes is raised, because of an 
increase in the "opsonins." The curve of the anti- 
bodies is like that usually obtained by active immu- 
nization with bacteria, toxins or other substances. 
Immediately following the inoculation there is a 
decrease even of normal antibodies. This "nega- 
tive phase/' according to Wright, lasts for from 
one to several days and corresponds to a period of 
increased susceptibility. Kussell and others have 
not observed this period of increased susceptibility. 
It is quickly followed by a positive phase in which 
the antibodies and, correspondingly, the resistance, 
increase rapidly. When very small doses are 
administered the positive phase may be recognized 
after twenty-four hours (Wright). Large doses 
cause a prolonged negative phase and are to be 
avoided. 

Following injection, "the local symptoms first 
make themselves felt after an interval of two or Reactions. 
three hours. The effects then seen are the develop- 
ment of a red blush and more or less serous exuda- 
tion at the site of inoculation, followed by some 
lymphangitis along the lymphatics which lead, ac- 
cording as the vaccine has been inoculated above 
or below the middle line of the trunk, in the direc- 
tion of the glands of the axillae or of the groin. 
. . . Even severe inflammation has never led on 
to suppuration." The exudate is somewhat hem- 
orrhagic, and the pain varies from moderate to 
severe, but is not of long duration. With the 
technic as recommended at present, "the constitu- 
tional symptoms are limited to some headache and 
to two or three hours of real malaise. . . . The faction. 



Local 



446 INFECTION AND IMMUNITY. 

next day his temperature comes down to normal, 
and he feels comparatively well except in respect 
to pain at the seat of inoculation." Of 5,473 sol- 
diers vaccinated against typhoid, twenty-one took 
the disease and two died. In 6,610 soldiers under 
similar conditions who were not vaccinated, there 
were 187 cases and twenty-six deaths (Leish- 
mann). The method of vaccination used by Kus- 
sell and his associates in the U. S. Army is similar 
to that of Wright, but three injections ten days 
apart are given, the first of 500 million, the second 
and third of one billion. No bad results have 
occurred in 8,510 cases, and the results have been 
satisfactory, not a single case of typhoid occurring 
in any one whose vaccination was completed. 
Among the unprotected in the army 200 cases 
developed in the same period of time. 

The vaccine was prepared as follows: A non- 
virulent strain of the bacillus is grown on agar, 
slanted in flasks for twenty-four hours. The 
growth is then emulsified in salt solution and 
standardized to contain 1 billion bacilli to 1 c.c. 

The vaccine is then sterilized by heating to 56° 
C. for one hour; 0.25 per cent, tricresol is added 
as a preservative and the sterility tested by aerobic 
and anaerobic cultures. The harmlessness is proved 
by inoculation into guinea-pigs and mice. 
conditions The adoption of antityphoid inoculation or vac- 
vaccination 1 ! cination under certain conditions appears to be 
warranted. Typhoid never has been a world pest; 
but in the presence of epidemics in densely popu- 
lated districts, the method may well be considered. 
The question is a pertinent one also for those cities 
in which typhoid is so extensive as to be called 
• endemic. It has a distinct field in the protection 



THERAPY. 447 

of troops in time of war, when it is difficult to 
observe other prophylactic measures, and should 
recommend itself to physicians and nurses during 
epidemics. 

The products of autodigestion of typhoid cul- 
tures have been suggested as suitable vaccine 
(Neisser and Shiga). The local reaction is said 
to be mild, and the body reacts by the formation 
of bactericidal amboceptors and agglutinins. 

Bactericidal serums obtained by the immuniza- serotherapy. 
tion of horses with typhoid bacilli have not shown 
distinct curative properties. Chantemesse im- 
munizes horses with a typhoid "toxin" which is 
prepared by growing the organism in a liquid cul- 
ture which contains an emulsion of splenic tissue. 
One cubic centimeter of this toxin will kill a 
guinea-pig, a dose which in comparison with 
other bacterial toxins is very weak. Chantemesse 
has used his antitoxic serum in the treatment of 
more than 500 patients, reporting a mortality of 
about 6 per cent., whereas that among untreated 
patients was from 10 per cent, to 12 per cent. 
Although these figures indicate some value for the 
serum, it has had little trial outside of France. 

MacFadyen and Eowland immunize horses with 
extracts of typhoid bacilli, which have been ground 
up while they were kept in a brittle state by the 
temperature of liquid air. Although antitoxic and 
bactericidal properties are claimed for the serum, 
there is no conclusive evidence that it differs from 
bactericidal serum prepared in the ordinary way. 

Jez produces a high degree of immunity in rab- Preparation 
bits by artificial immunization with the typhoid 
bacillus, then prepares an extract from the spleen, 
bone marrow, brain, etc., of the immunized ani- 



448 INFECTION AND IMMUNITY 

mals. The extract is administered by mouth. Jez 
justifies this method, from the fact that the lym- 
phoid organs have been shown to form typhoid 
antibodies (Wassermann). From the clinics of 
Eichorst and others favorable reports concerning 
the remedy have been published. It has had no 
extensive use. The preparation is made by the 
Serum Institute of Berne and is expensive. The 
suggestion of Fraenkel, that typhoid patients be 
treated by subcutaneous injections of small quan- 
tities of killed typhoid bacilli in order to hasten 
the formation of antibodies has been kept alive 
through the "typhoin" of Petruschky, but has not 
had practical trial. Of a similar nature is the sug- 
gestion of Kichardson, that the filtrates of typhoid 
cultures be injected. Eichardson reports unsatis- 
factory results with various preparations of typhoid 
bacilli, including the non-toxic split products of 
Vaughan. 

Anders has concluded from his results following 
the injections of killed typhoid bacilli, that the 
procedure is of value only in cases of relapse and 
in bacillus-carriers in order to rid the person of 
the bacilli. Doses of from 25 to 50 million bacilli 
were used and the injections were repeated every 
three days. 
Assintina- The principles and technic of the agglutination 
tlon ' test were described in Part I. The serum 
commonly becomes agglutinating on from the 
seventh to the tenth day, rarely as early as the 
second or third, and as late as from the twentieth 
to the fortieth day. The power is highest during 
convalescence, when it may agglutinate in dilu- 
tions as high as 1 to 5,000 or higher, and from 
that time sinks gradually. An agglutinating 






PARATYPHOID. 449 

power of 1 to 160 has often been found at eight 
months, and of 1 to 50 after from seven and one- 
half to eleven years; but the latter duration is not 
the rule. In performing the test, a serum dilution 
of not les than 1 to 40, or 1 to 50 should be 
observed as previously set forth. 

The following sources of error are to be borne 
in mind: Typhoid fever occasionally runs its 
course without the formation of agglutinins; the 
reaction may mysteriously be absent one day to 
recur a few days later, a condition which indicates 
the importance of repeated tests; rather high ag- 
glutinating power for the typhoid bacillus occa- 
sionally develops in other infections, as pneumo- 
nia, meningitis, icterus, Weil's disease, etc.; the 
possibility of group agglutination, for the positive 
elimination of which control tests with related or- 
ganisms maj be demanded. In case negative 
results are obtained in a suspicious case, the reac- 
tions should be tried with the paratyphoid bacilli. 
The test of the bactericidal powers of the serum 
has been recommended as a substitute for the ag- 
glutination reaction, but the technic is so much 
more complicated that the method will probably 
not come into general use. For diagnosis previous 
to the formation of agglutinins, blood-cnltures 
should be made as described in a preceding para- 
graph. 

II. PARATYPHOID FEVER. 

In 1900 Scholtmiiller cultivated from the blood 
of five "typhoid" patients organisms which differ 
from the typhoid bacillus in that they attack dex- 
trose with gas formation and are not agglutinated Baciiii, 
in high dilution by antityphoid serum. Since 



Paratypho id 
and 
Paracolon" 






450 IXFECTIOX AXD IMMUXITY. 

then, similar cases have been reported and two 
types of the paratyphiod bacillus have been recog- 
nized (SchottmiiHer). Bacilli of Group B cause 
first an acid reaction in milk which changes 
to a permanently alkaline reaction in about ten 
days, whereas those of Group A cause permanent 
acidity (Kayser). They resemble the typhoid 
bacillus morphologically, but culturally are more 
closely related to Bacillus enteritidis. Organisms 
which have previously been described as "para- 
colon" bacilli (Widal, Gwyn) do not differ from 
those which are now called paratyphoid bacilli, 
and the infections caused by them resembled the 
recorded cases of paratyphoid fever. The term 
"paracolon" should no longer be applied to them. 
Paratyphoid fever occurs sporadically or in epi- 
oiogy. demic form, and bears a close resemblance to mild 
typhoid-like epidemics which have been noted from 
time to time, and which, presumably, are caused 
by eating poisonous meats. One such epidemic of 
600 cases was caused in Switzerland in 1878 by 
the meat of a sick calf; the mortality was 1 per 
cent. A still older epidemic (1839) is cited, like- 
wise caused by meat. In both instances the infec- 
tion eventually was carried from person to person 
by contact. A recent outbreak in Kiel, proved to 
be paratyphoid, is assumed by Fischer to have been 
caused by infected meat, on account of the peculiar 
distribution of the cases among the patrons of a 
particular market. Kurth also attributed a small 
epidemic to either uncooked meat or milk. Fischer 
mentions fifty cases in East Holstein probably 
caused by the milk of two cows. Shortly after the 
epidemic began, the cows died and paratyphoid 



Epidemi' 



PARATYPHOID. 451 

bacilli were cultivated from the muscles, spleen, 
liver and intestines. De Feyfer cites an instance 
in which the disease apparently was transmitted 
through the water of a stream in which the cloth- 
ing of the first patients had been washed. In 
another instance, a regimental infection was traced 
to the discharges of a single soldier, the water sup- 
ply having become contaminated through a defec- 
tive water closet. 

Paratyphoid, like typhoid fever, is accompanied ciiaracter- 
by an enlarged spleen and many rose spots. Al- Disease. 
though severe symptoms may be present for a time, 
the course of the disease usually is mild and the 
mortality is low. The incubation period approxi- 
mates that of typhoid. In the few cases which 
have come to autopsy the intestinal lesions have 
varied from a mild ileocolitis with an intact mu- 
cous surface to a condition of superficial ulcera- 
tion. The involvement of Peyer's patches and the 
solitary follicles which is so characteristic of ty- 
phoid is absent, although these structures may be 
moderately swollen. The mesenteric lymph glands 
are not markedly involved and there is little pro- 
liferation of the lymphoid or endothelial cells 
(Wells and Scott). The disease has no specific 
anatomic lesion. 

The organisms are found in the blood and vari- Excretion, 
ous organs, yi the rose spots, urine and feces of the an^mSri- 
patients. Practically nothing is known of the oc- bTlti<m - 
currence of the bacilli outside the body. Because 
of their presence in the stools and urine of the pa- 
tients, the methods of dissemination and infection 
doubtless are similar to those concerned in typhoid. 
The bacillus is said to have a marked resistance to 
heat, withstanding 60° C. for 30 minutes and 



452 INFECTION AND IMMUNITY. 

not all cells being killed during one hour at 
this temperature. This may explain the fact that 
the virus is not always killed by cooking the meat. 
The organism probably has a wide distribution 
because of the occurrence of the infection in vari- 
ous parts of the world. 

The toxicity of the bacilli depends on the exist- 
ence of a fixed endotoxin; a soluble toxin is not 
produced. The principles of prophylaxis against 
typhoid also apply to paratyphoid fever, with the 
addition that in the latter disease the possibility of 
meat infection must be kept in mind. 

The serums of patients and immunized animals 
acquire bactericidal, opsonic and agglutinating 
powers for the organism. There is no serum ther- 
apy for the infection, nor has the occasion arisen 
to attempt vaccination. 
Aggrintina- Serum from a paratyphoid patient may aggluti- 
Biood nate the homologous bacillus in a dilution of 
1/1000 or 1/2000 or more (E. H. Buediger), 
whereas the typhoid bacillus is agglutinated only 
in low dilutions by the same serum. How- 
ever, bacillus A and bacillus B are not identical 
in their agglutinable properties; in this respect 
it is stated that the latter is more closely re- 
lated to the typhoid bacillus than the former. 
The agglutination test is said to have a higher 
diagnostic value than the Gruber-Widal reaction 
in typhoid, a stronger agglutinating power being 
developed in the serum of the patient. Never- 
theless, the formation of coagglutinins may render 
the test confusing if proper serum dilution is not 
practiced. Conclusions should not be attempted 
until the test has been performed with both strains 
of the paratyphoid bacillus and with the typhoid 



Cultures. 



D YSEK TEH Y BA CILL US. 453 

bacillus. As in typhoid, early diagnosis may be 
best accomplished by bacteriologic examination of 
the blood. 

III. ACUTE EPIDEMIC DYSENTERY. 

In addition to amebic dysentery, we have de- 
come familiar with an acnte dysenteric infection 
which appears epidemically in both tropical and 
temperate climates, and prevails especially in the 
summer months. Such epidemics occur extensively 
in Japan, where the mortality may be 24 per cent. ; 
in the Philippines, United States, Germany and 
other European countries. In industrial settle- 
ments in Germany the mortality is about 10 per 
cent. (Kruse). The incubation period may be as 
short as two or three days. In mild cases the pa- 
tient may recover in from four to eight days, 
whereas severe cases last from two to four weeks, 
and may terminate fatally. Occasionally the in- 
fection lasts sufficiently long to be considered 
chronic. 

In 1898, Shiga, basing his conclusions on posi- 
tive results with the agglutination test and on the 
constant presence of the organism in the stools of 
the infected, identified as the cause of the disease, 
in Japan, a microbe which is known as Bacillus 
dy sentence. (Shiga). Flexner, in 1900, made simi- 
lar observations on epidemic dysentery in Manila, 
and his organisms, or one of them, differing slight- 
ly from that of Shiga, is called Bacillus dysenteric 
(Flexner), or the Flexner-Harris bacillus, Harris 
being the name of a patient from whom this 
typical strain was cultivated. Kruse (1901) found 
both the Shiga and Flexner types in Germany, 
needlessly giving the name of "pseudodysentery" 
bacilli to the latter. In this country similar organ- 



454 INFECTION AND IMMUNITY. 

summer isms have been found as the cause of institutional 
Diarrheas, dysentery by Vedder and Duval, of summer diar- 
rheas of infants by Duval and Bassett, and by Wol- 
stein. It is the belief of Vedder and Duval that 
acute dysentery, the world over, "whether sporadic, 
institutional or epidemic, is caused by the dysen- 
tery bacillus." We must note, however, that the 
organism is not found in all cases of clinical dys- 
entery, even by skilled bacteriologists. "Clinically, 
24 of our 97 cases in which the dysentery bacilli 
were found did not differ from the cases of ileocoli- 
tis in which the dysentery bacilli were not found." 
(Weaver and others.) It seems certain, neverthe- 
less, that Bacillus dysenterice is the most impor- 
tant cause of acute dysentery. It rarely occurs in 
the stools of healthy individuals. 

The organisms of Shiga and Flexner differ in 
their actions on the sugars mannite and maltose 
(i. e., in their acid-forming powers) and in their 
agglutinability ; the "Flexner" type is the stronger 
acid-former. An artificially produced immune se- 
rum which is specific for one organism has rather 
higher agglutinating and bactericidal _ powers for 
the corresponding type, but low for the other. In 
this country the "Flexner" bacillus is much more 
common than that of "Shiga," but here and abroad 
both types are met, and sometimes in the same 
individual. Several other organisms have been 
cultivated from dysenteric patients, but the varia- 
tions from these two types are slight. All are 
certainly very closely related. 
character- ^he organism is somewhat thicker than the 
tii i! B ics -iii f typhoid bacillus, but probably is non-motile, al- 
though Vedder and Duval, in opposition to others 
(Lentz), claim to have demonstrated flagella. It 



DYSENTERY BACILLUS. 455 

often shows a polymorphous appearance in cul- 
tures, but forms no spores. It is Gram-negative. 
It lives for from 12 to 17 days when dried 
(Pfuhl) ; direct sunlight kills it in 30 minutes, 
1 per cent, phenol in 30 minutes, 5 per cent, phenol 
plus corrosive sublimate (1/2000) almost instan- 
taneously. It is thought that it may live over 
winter and cause fresh outbreaks in the spring 
(Kruse). 
The bacillus is found only in the stools of the Distribution 

•> . in the Body. 

.infected, in the mucous or muco-hemorrhagic por- 
tions of which it exists almost in pure culture, few 
colon bacilli being in the immediate vicinity; it 
has not been found in the blood or urine. In fatal 
cases, Shiga found it only in the intestinal ulcers 
and swollen lymphoid structures and in the mesen- 
teric lymph glands. Flexner mentions its occur- 
rence in the liver. The organism, if it reaches the 
circulation at all, either does so in small quantities, 
or is rapidly destroyed by the blood. The infection 
resembles cholera, but differs from typhoid and 
paratyphoid in this respect. An observation by 
Markwald (cited by Lentz) indicates, however, 
that the bacilli may reach the circulation. A 
woman ill with dysentery gave birth to a child, 
which died within a few hours. Dysenteric changes 
were found in the intestines, and the bacillus of 
dysentery was cultivated from the diphtheritic de- 
posits on the intestines, from the meconium and 
from the heart's blood. The organisms must have 
reached the child through the placenta from the 
circulation of the mother. 

The intestinal lesions vary from a simple in- Lesions. 
flammatory hyperemia to rather extensive superfi- 
cial necrosis (diphtheritic inflammation), which 



456 



INFECTION AND IMMUNITY. 



Toxicity of 

Organisms. 



rarely extends below the submucosa. Such foci 
are said to be the most marked in the descending 
colon and sigmoid where mechanical injury is 
more likely to occur. The necrotic areas separate 
by sloughing, leaving superficial ulcers. The lym- 
phoid follicles are swollen and infiltrated with 
polymorphonuclear leucocytes, which also accumu- 
late in the dilated lymph spaces of the intestinal 
wall. The ileum is so commonly involved that the 
condition is called an ileocolitis. Conspicuous 
changes are not found in the mesenteric glands or 
spleen. The liver and kidneys commonly show 
par en ch y matous degenerations. 

The dysentery bacillus is highly toxic. Subcu- 
taneous injections of killed cultures produce in 
man a more profound reaction than the organism 
of either cholera or typhoid. Ordinary laboratory 
animals are so susceptible that they are immunized 
with difficulty; the horse is less susceptible. The 
toxicity of the organism apparently depends on an 
intracellular toxin (an endotoxin) rather than on 
a soluble toxin. When living or killed cultures 
are submitted to autodigestion in salt solution 
(Conradi, Neisser and Shiga), or when bouillon 
cultures are allowed to grow for 30 days, the 
liquids are found to be toxic after the organisms 
are removed. In both instances this toxicity prob- 
ably depends on the liberation of endotoxins. The 
question as to whether the bacillus in the intes- 
tines produces a soluble toxin which is absorbed by 
the lymphatics, is undetermined. It seems more 
probable that the conditions are analogous to those 
of cholera, intoxication resulting from the libera- 
tion of endotoxins by the solvent action of the tis- 
sue fluids or cells on the bacilli. Dysenteric symp- 



I 



PROPHYLAXIS. 



457 



toms are not produced in animals by feeding the 
organisms. 

The stools of the patient are the only known 
source of the organism and it continues to be ex- 
creted during convalescence. Latent or chronic 
cases are a source of danger to a community. Al- 
though the conditions outside the body are not 
favorable for the growth of the organism, it may 
remain living and virulent for several months. The 
methods of infection appear identical with those 
in typhoid. "Water infection seems certain, and 
indirect transmission is accomplished by contact 
with the discharges. The best examples of contact 
infection are found in institutional epidemics. 

The first essential for prophylaxis is correct di- 
agnosis, for which the agglutination test and bac- 
teriologic examination of the stools are essential . 
Disinfection and other precautions should be prac- 
ticed as rigidly as in typhoid. The patient should 
not be discharged until the stools are free from 
dysentery bacilli. 

Poorly nourished individuals are particularly 
susceptible to infection, and among them the mor- 
tality is high. The disease is most common among 
young children, old people, and those who are con- 
fined in institutions. The conditions in Japan, 
however, where from June to December of one year 
nearly 90,000 were attacked, and in Germany, 
where severe epidemics occur in industrial com- 
munities, indicate that susceptibility is quite gen- 
eral. Digestive disturbances and enteritis from 
other causes are said to be predisposing factors. 
The normal serums of man and animals have very 
little bactericidal power for dysentery bacilli. 



Dissemina- 
tion and 
Infection. 



Prophylaxis 
and Suscep- 
tibility. 



458 



INFECTION AND IMMUNITY. 



Vaccination 

and Serum 

Therapy. 



The subject of acquired immunity to dysentery 
is hardly on a satisfactory basis. The serum of 
convalescents shows a distinct bactericidal and op- 
sonic power for the organism, and there is good 
reason to believe that the acquired immunity per- 
sists for some time after the disappearance of the 
bactericidal amboceptors and opsonins, an event 
which takes place rather early. As in typhoid, 
animals which through immunization have once 
been stimulated to produce antibodies, form them 
much more readily on the occasion of a subsequent 
inoculation. This acquired facility in producing 
antibodies may be a factor in acquired immunity. 
By immunizing horses, serums of rather high pro- 
tective power have been obtained. Kruse prepared 
a serum of which 1/80000 gram would save a 
guinea-pig from a dose of the bacilli which killed 
a control in 20 hours. It is assumed that the pro- 
tective power of this serum is due to its bactericidal 
action. The antitoxic serum which Eosenthal pre- 
pared, by immunizing with 30 days' old bouillon 
cultures, protected not only against the toxin, but 
also against the bacilli; and conversely an anti- 
bacterial serum protected against the toxin (cited 
by Lentz). Such results leave us very much in 
doubt as to the existence of a true antitoxic serum. 

The value of protective inoculations is not well 
established. Shiga at one time practiced mixed 
active and passive immunization (bacilli plus im- 
mune serum) on 10,000 individuals. This did not 
decrease the number of infections, although a lower 
mortality resulted. Shiga claims that the thera- 
peutic use of his serum reduces the mortality to 
one-third that of the untreated. The serum of 
Kruse, and also that of Eosenthal, are said to be 



AGGLUTINATION. 459 

curative ; the discharges rapidly decrease in rmmber 
and the course of the disease is shortened. In the 
Rockefeller Institute for Medical Research anti- 
dysentery serum proved of no distinct value. 

The agglutination reaction with the serum of Agginiina- 
patients shows great variability. It is sometimes 
absent in spite of the presence of bacilli in the 
stools, and often disappears rapidly during con- 
valescence (in two weeks occasionally). It is rarely 
as high as in typhoid. In infantile diarrheas ag- 
glutinins appear at about the end of the first week 
of illness (Duval and Bassett). Evidently mild 
eases in which the course of the disease is from 
four to eight days may not be recognized by means 
of the agglutination reaction before the period of 
convalescence. In chronic cases the agglutinating 
power may persist for three or four months. No 
reaction was obtained with the typhoid bacillus. 
Kruse considers the reaction diagnostic when it 
occurs in a dilution of 1/50 ; Pfuhl, 1/30. Strong 
co-agglutinins for other organisms, i. e., above 
1/50, have not been observed (Lentz). The tests 
should always be performed with both the "Shiga" 
and "Flexner" types, as the two have not identical 
agglutinable properties, and either organism may 
be the cause in a given instance. The absence of 
the reaction does not exclude a dysenteric infec- 
tion positively. Bacteriologic examination of the 
stools is important, often necessary, for early diag- 
nosis. 

IV. MEAT POISONING BY BACILLUS ENTERITIDIS. 

Botulism as a special form of meat poison- 
ing and the occasional production of paratyphoid 
by infected meats, have been mentioned. In 
addition to these, more or less extensive epidemics, 






Enteritiflis 



460 INFECTION AND IMMUNITY. 

supposed to be due to ptomains which were found 
in putrid meat, have occurred not infrequently. 
It is now well established that most epidemics of 
this character are caused by pathogenic bacteria 
which are present in the meat, putrid decomposi- 
tion of the latter being an unessential incident. 

Gartner, in 1888, had the opportunity of study- 
ing an epidemic caused by the meat of a cow which 
had been slaughtered in extremis. The symptoms 
differed from those of botulism or paratyphoid, as 
described below. He obtained from the muscle and 
spleen of the cow, and from the spleen of a man 
who had been fatally poisoned, an organism which 
has since been known as Bacillus enteritidis (Gart- 
ner). The same bacillus, or organisms which re- 
semble it closely, have been obtained repeatedly 
during similar epidemics, both from the suspected 
meat and from the organs in fatal cases (intes- 
tines, blood, spleen, etc.). Drigalski, from a com- 
parative study of several strains obtained from dif- 
ferent sources, concluded that all are members of a 
closely related group of organisms, the group of 
Bacillus enteritidis. His conclusions were based 
on cultural properties and agglutination tests. 

The typical organism is a short rod, often ovoid 
in shape, possesses from four to twelve long flag- 
ella and has moderate motility. It ferments vari- 
ous sugars and is not stained by Gram's method. 
Variations among individual strains need not be 
discussed here. 
ratuo- According to v. Ermengem, and also Drigalski, 
its pathogenicity depends on the elaboration of a 
soluble but heat-resistant toxin. Bouillon cul- 
tures twelve days old, in which the bacteria have 
been killed by heat, also similar cultures from 



Seincity. 



BACILLUS ENTEBIT1DI8. 461 

which the bacteria have been removed by filtration, 
are toxic for mice and guinea-pigs (Drigalski). It 
is noteworthy, however, that relatively large quan- 
tities of the bouillon were necessary to kill guinea- 
pigs (4.0 c.c.) which is in contrast to the toxins of 
diphtheria and tetanus. The rapidity with which 
symptoms develop following the ingestion of in- 
fected meat is a further indication of the exist- 
ence of this soluble toxin, which, it would seem, is 
formed in considerable quantities in the meat. 
Symptoms occasionally develop so quickly as 
to suggest some strong metallic poisoning. With- 
in a few hours vomiting, violent diarrhea and 
colicky pains set in, followed by more or less 
collapse, weakness, headache and not uncom- 
monly by erythematous, urticarial or herpetic 
eruptions. Fever is absent or inconspicuous. 
The mortality is not high, from 2 to 5 per cent.; 
convalescence is said to be slow. Nephritis and 
catarrhal pneumonia have been noted as sequelae. 
Autopsy shows the anatomic changes of an acute 
gastroenteritis, sometimes of hemorrhagic charac- 
ter, with swollen Peyer's patches; the large intes- 
tine is not greatly involved. The spleen may be 
swollen and the kidneys degenerated. The ana- 
tomic findings are not specific. 

It has been shown in numerous instances that sources of 
the cattle or horses (Drigalski) which furnished 
the meat. were sick with an intestinal or general 
infection with Bacillus enteritidis before they were 
slaughtered. "In a very large number of cases it 
can be demonstrated that the animals from which 
the meat was taken had been slaughtered in 
extremis or had died recently, and, indeed, that 
thev had (in certain instances) died before they 



Infection. 



INFECTION AND IMMUNITY. 



Growth in 
the Meat, 



Toxin in 
Meat. 



could be slaughtered. Most often they suffer from 
septic inflammatory processes or from traumatic, 
puerperal or other sorts of septicemia, or from 
other ill-defined pathologic conditions which are 
accompanied by symptoms of enteritis or intestinal 
or pulmonary inflammations" (v. Ermengem). 
Subsequent infection of the meat by Bacillus en- 
teritidis. i. e., after slaughtering, has not been 
noted. 

The organism occurs in the blood and various 
organs of infected animals and man. Poisoning 
most commonly arises when the meat has been 
kept for several days, which usually is the case by 
the time it is made into some form of sausage. In 
the meantime the bacilli have proliferated and ad- 
ditional toxin has been produced. In at least one 
instance a certain number of patients who ate the 
meat while it was fresh suffered moderate or no 
intoxication, whereas those who ate it several days 
later became violently ill. In an epidemic caused 
by horse meat Drigalski found that "only those 
persons suffered from intoxication who ate the 
meat after it had lain for eight days or more." 

The micro-organism is very resistant to heat 
and the temperature which is attained in ordinary 
cooking may not be sufficient to kill the bacteria 
which are remote from the surface. Even in the 
event that the meat has been thoroughly sterilized, 
the heat-resistant toxin may be present in suffi- 
cient quantity to cause the intoxication. Not 
much is known concerning the distribution of 
Bacillus enteritidis. v. Ermengem suspects that 
it may be a factor in poisoning by oysters and fish, 
but this remains undetermined. 



COLON BACILLUS. 



463 



The blood acquires specific agglutinins during Agglutinins. 
the course of infection. Even eight days after the 
beginning of sj^mptoms agglutination may be ob- 
tained in dilutions varying from 1/200 to 1/4000. 
The agglutinins disappear very rapidly. Working 
with artificially prepared immune serum, Drigal- 
ski determined the existence of coagglutinins for 
typhoid and paratyphoid bacilli. 

We should bear in mind the likelihood that 
meats poisoned with Bacillus enteritidis, as well as 
by paratyphoid bacilli, may be encountered in 
America, as well as in foreign countries. 

V. BACILLUS COLI 

Bacillus coli, or the colon bacillus, is the type of 
a large group of organisms the members of which 
show individual differences, but possess certain 
dominant features in common. The typical colon 
bacillus ferments various sugars, with the produc- 
tion of gas, is a strong acid producer and curdles 
milk. It is flagellated, has moderate motility and 
does not stain with Gram's method. One type or 
another is the normal inhabitant of the intestinal 
tract of many animals, and, although the organ- 
isms are widely disseminated in nature, their 
occurrence is related directly or indirectly to the 
distribution of feces. 

Its optimum temperature for growth is 37° C, Agglutinins. 
and above 46° C. it does not proliferate. It is 
killed at a temperature of from 60° to 61° C. in 
from five to fifteen minutes; it is not killed by 
such low temperatures as from — 20° to — 24° C. 
It resists absolute desiccation for periods varying 
from a few days to several months (different ob- 
servers). Direct sunlight kills 99 per cent, of the 
germs in two hours (Billings and Peckham), and 



464 



INFECTION AND IMMUNITY. 



Distribution 

in the 

Intestines. 



Normal 

Functions. 



they are very susceptible to ordinary antiseptics. 
The normal serums of many animals are bacterici- 
dal for the colon bacillus. 

Escherich, the discoverer of this organism, lays 
down the principle that that strain which may 
be cultivated from the feces of the nursing child 
should be considered as the typical Bacterium coli 
commune, maintaining that a constant type of or- 
ganism is found under these conditions. It is said 
to occur here in relatively pure culture. 

Within a very short time after birth the organ- 
ism is found in the intestines of infants, and its 
method of entrance has been the subject of much 
discussion. In view of its ready dissemination it is 
not difficult to conceive of many circumstances 
which favor its entrance. Having once reached 
the intestines, it finds there its optimum conditions 
for growth. The small intestines in man are 
rather free from colon bacilli and other organisms 
as well. This, perhaps, is due, to some extent, to 
the alkalinity of the medium and to the rather 
rapid flow of the intestinal contents at this point. 
The colon bacillus reaches its maximum develop- 
ment in the large intestine, where, in fact, the 
whole bacterial flora of the intestines is most con- 
centrated. 

In view of the fact that the colon bacillus is a 
normal inhabitant of the intestines, the conception 
has occurred to many that it may be of distinct 
value to the economy, either because of the action 
it has on certain foods (splitting of carbohy- 
drates), or because in some obscure way it in- 
fluences favorably the assimilation of foods, or in 
that it antagonizes other bacteria of distinct patho- 
genic powers which also exist normally in the in- 



FUNCTION OF COLON BACILLUS. 465 

testines or reach them through accident. This is 
not the place to consider these questions in detail, 
and they are on none too definite a basis. It may 
be stated, however, that the colon bacillus and an- 
other closely related organism. Bacillus [lactis] 
aerogenes, distinctly antagonize the action of cer- 
tain proteolytic bacteria which appear to be associ- 
ated with the putrid decomposition of milk and 
other proteid-containing foods. Bacteria of the 
latter type exist in the intestines. Unsterilized 
milk has a natural resistance to putrid decomposi- 
tion, and sterilized milk to which the colon bacillus 
or Bacillus [lactis^ aerogenes has been added, has 
a similar resistance. These two bacteria flourish 
in the presence of carbohydrates, which they 
decompose with the liberal formation of acids, and 
through these acids they "limit intestinal putre- 
faction and influence (favorably) pathologic proc- 
esses which are caused or maintained by the 
existing 'alkaline fermentation'" (Escherich and 
Pfaundler). That the organisms in question 
antagonize the action of putrefactive bacteria has 
been shown in test-tube experiments (Hirschler). 

Since the time that v. Emmerich upheld thi JeSSti 
colon bacillus (or a colon-like microbe) as tht 
cause of Asiatic cholera (1885), opinion as to the 
pathogenic powers of the organism has undergone 
many fluctuations. Following Koch's demonstra- 
tion of the comma bacillus as the etiologic factor 
in cholera, the colon bacillus was, so to say, re- 
pressed as a pathologic agent. Later, and especially 
in France, great significance was again attached to 
it. The condition still shows a great deal of chaos, 
although, on account of more refined technic and 
the elimination of other organisms, as the dyseu- 



genicity. 



466 INFECTION AND IMMUNITY. 

tery and paratyphoid bacilli and Bacillus enteriti* 
dis, from the colon group proper, we are, perhaps, 
on the way to a more satisfactory understanding 
of the pathogenicity of this organism. Although 
certain authors hold at the present time that the 
colon bacilli which normally inhabit the intes- 
tines are devoid of virulence, such a radical posi- 
tion is open to question. Avirulent strains have 
often been encountered, however. 

virulence Harmless as the colon bacillus appears to be 
when confined in the intact intestines, its viru- 
lence for animals, although low, has been demon- 
strated in many instances. A bouillon culture of 
the average bacillus which has grown for from one 
to two days, and when freshly cultivated from the 
stools, causes the death of a 300 to 400 gram 
guinea-pig in two or three days, when given intra- 
peritoneally in a dose of from 2 to 3 c.c. Subcu- 
taneous inoculations, the feeding of cultures, their 
introduction into the bladder and biliary passages 
induce inflammatory processes. It is stated 
(Escherich) that whether the cultures are intro- 
duced into the skin, peritoneum or vessels, symp- 
toms of severe gastroenteritis are produced, not 
unlike Asiatic cholera. This fact doubtless in- 
fluenced v. Emmerich in considering the organism 
as the cause of cholera. The general symptoms are 
those of an acute febrile intoxication. 

The organism is most pathogenic when freshlv 
cultivated, and soon loses its virulence after re- 
peated transplantations. As in the case of some 
other bacteria, virulence may be re-established by 
"passage" through suitable animals. 

virulence The cultivation of the colon bacillus from the 
an * blood and organs of man at autousv has not the 



COLON BACILLUS INFECTIONS. 467 

significance which was once attached to it. It has 
been recognized that the colon bacillus in particu- 
lar, and less commonly other intestinal organisms 
may enter the circulation a short time before death, 
at a time when resistance is very low, and may 
obtain the general distribution which is so often 
encountered at autopsy ; this is the so-called "ago- 
nal invasion," which may occur without much re- 
gard to the primary cause of death. The condi- 
tions which favor agonal invasion remain, to a 
large extent, obscure. Distinct defects of the in- 
testinal mucosa probably are not essential, al- 
though this view has its representatives. In states 
of low vitality in which resistance to infection is 
decreased (disappearance of complement), the or- 
ganisms find conditions favorable to proliferation 
when they have once reached the circulation. In 
spite of the low virulence of the colon bacillus, it 
commonly has a certain amount of toxicity and it 
may often be of significance even as an agonal in- 
fection. 

Post-mortem invasion of adjacent structures, as 
the gall bladder and liver through the biliary pas- 
sages, and of the peritoneum through the intesti- 
nal wall, also occurs. 

It has been shown that the colon bacillus occa- True 
sionally causes the following conditions : Suppura- 
tive cholecystitis which may extend to the liver, 
peritonitis, septicemia, meningitis, cystitis, pyeli- 
tis and ascending suppurative nephritis, and ab- 
scesses in various organs, including suppurative 
processes in the middle ear. In one or more in- 
stances it has been thought that it caused vegeta- 
tive endocarditis. Probably colon infections of the 
gall bladder do not occur in the absence of biliary 



Infections. 






468 INFECTION AND IMMUNITY. 

stasis. Ordinarily cases of peritonitis in which 
the colon bacillus is encountered also show the 
presence of other pathogenic organisms, as strepto- 
cocci or staphylococci; this is always the case in 
perforation peritonitis. Doubtless wrong conclu- 
sions have been drawn in many instances as to the 
bacteriology of peritonitis from the fact that the 
colon bacillus readily overgrows many other bac- 
teria in culture media. 
cystitis. Escherich attributes great importance to this or- 
ganism as the cause of cystitis, especially in chil- 
dren, and states that it is probably the most com- 
mon cause of cystitis, pyelitis and ascending sup- 
purative nephritis. In fifty-eight of sixty cases of 
cystitis in children the colon bacillus was found 
either alone or in mixed cultures. An increased 
agglutinating power of the patient's serum for the 
organisms cultivated from the urine is noted in 
these cases. Davis and others have described cases 
of urinary infections due to B. eoli differing from 
the usual type in that the growth on various media 
is less luxuriant and milk is not coagulated. 

Davis has found that the serum of patients with 
such infections may be high in opsonic power and 
low in bacteriolytic, or vice versa. 
iarrheas. Great interest attaches to the colon bacillus in 
relation to enterocolitis and dysenteric diseases. 
Escherich speaks of an enteritis follicularis, or 
colitis contagiosa, or colicolitis, epidemics of which 
have been noted at different times. A number of 
these epidemics occurred before the identification 
of the dysentery bacillus, and certain of them may 
have been true dysenteric infections. Neverthe- 
less, dysentery bacilli are not found in all cases of 
enterocolitis, and the probability that genuine 



CHOLERA. 469 

cases of colon enteritis occur can not as yet be neg- 
lected. 

A specific colon toxin has not been obtained. 

Immunization with the colon bacillus causes the 

formation of bactericidal amboceptors, opsonins 

and agglutinins. 

Not all strains of the colon bacillus are identical Agglutina- 
tion. 

in their agglutinogen^ receptors. A serum which 

agglutinates one colon strain does not necessarily 
agglutinate all strains. The reaction, according to 
Paltauf and others, is largely an individual one. 
The serum of a patient with a colon infection will 
agglutinate the strain causing the disease, but may 
not affect other strains. Hence, for diagnostic 
purposes, the test must be performed with the cul- 
ture which has been obtained from the patient. 
Pfaundler says in reference to colicolitis that if 
other colon infections can be excluded, and if the 
serum of the patient gives the agglutination reac- 
tion in a dilution of 1 to 50 with the bacillus 
which has been cultivated from the stools, colon 
infection is indicated (Paltauf). 

Vaccine therapy has been successfully applied to |5 1 %® i ^ lc 
many of these colon bacillus infections. The 
autogenous organism should always be used owing 
to variation in the bacilli, especially in infections 
of the urinary tract. 

VI. CHOLERA. 

In 1883 Koch discovered the Vibrio cholerce and 
cultivated it from the stools of cholera patients. 
The organism may be cultivated from the stools of 
the patients invariably, and is never found in other 
diseases nor in normal stools, except in the case of 
non-susceptible persons who may be encountered 






470 INFECTION AND IMMUNITY. 

during an epidemic. The latter are a source of 
danger as "cholera carriers." 
ciiaracteris- Typically the cholera vibrio is about 1.5 microns 
organism, long and one-fourth as broad. The cells of young 
cultures have the so-called comma shape which has 
given the organism the name of the comma bacil- 
lus. The form in reality is that of a segment of a 
spiral. When two cells are attached end to end an 
S-shape may be produced, and long spirals are 
made up of many cells which are joined at the 
ends. In old cultures the cells may assume the 
form of thick rods or even appear coccus-like. The 
vibrio possesses a single long flagellum, which is sit- 
uated at the end. Although two, four and six flag- 
ella have been described, Kolle states that such or- 
ganisms are vibrios of another nature. In the 
character and rapidity of their movement, as seen 
in a hanging-drop, Koch compares them to a 
swarm of mosquitoes. Old cultures may lose their 
motility to a large extent. The cholera vibrio 
does not form spores, although certain involution 
forms simulate them. It stains readily with the 
ordinary anilin dyes and is Gram negative. 
cultivation The comma bacillus grows readily in alkaline 
stools, culture media with characteristic appearances; it 
is an obligate aerobe under artificial conditions, in 
spite of the fact that it nourishes in the intes- 
tines. The optimum temperature lies between 30° 
and 40° C. A very simple method of obtaining the 
organism in pure culture from the stools was dis- 
covered by Koch. In tubes of peptone bouillon 
which have been inoculated with the feces of a 
patient, the vibrio proliferates rapidly and within 
a few hours exists in almost pure culture at the 
surface of the liquid. Isolated colonies are ob- 



CHOLERA VIBRIO. 471 

tained by transferring a small amount of the sur- 
face fluid to tubes of liquefied gelatin, then plating 
the latter. The colonies appear in a few hours as 
small translucent points from which pure cultures 
are made on a suitable medium. For more positive identifica- 
identification agglutination tests are performed tion ' 
with anticholera serum. The Eoyal Institute for 
Infectious Diseases (Berlin) keeps on hand a dried 
serum of known strength (1-10,000) for this pur- 
pose. The tests being made with high dilutions, 
coagglutinins for other vibrios are practically elim- 
inated. To the agglutination test may be added 
the "Pfeiffer experiment," in which the protective 
power of an anticholera serum is determined when 
guinea-pigs are infected intraperitoneally with the 
suspected culture. If the serum shows a protective 
power against this organism which approximates 
that shown against a known cholera vibrio, or, if 
the organisms are dissolved, the diagnosis of chol- 
era is justified. In performing such experiments 
the serum is mixed with the culture before injec- 
tion. 

The resistance of the cholera vibrio is very low. Resistance. 
It dies in about two hours when dried (Koch) and 
on this account dust infection is thought not to 
occur. It is killed instantly by the boiling tem- 
perature, and in five minutes at 80° C. It is ex- 
tremely susceptible to carbolic acid (killed by 1 
per cent, in five minutes), corrosive sublimate (1 
to 2,000,000 or 3,000,000 in from five to ten min- 
utes), and to acids. Calcium chlorid is an effi- 
cient disinfectant when thoroughly mixed with the 
stools. The micro-organism lives in distilled water 
not longer than twenty-four hours, in ordinary 
water for several days to several weeks, and in one 



472 INFECTION AND IMMUNITY. 

instance it was cultivated from the water of an 
aquarium after several months. Its life is short in 
the presence of putrefactive bacteria and rapidly- 
growing saprophytes, dying in sewer water in from 
twenty-four to thirty hours (Koch). Because of 
the large overgrowth of other organisms, the vibrio 
can rarely be cultivated from the stools later than 
from one to three days after death. Its life in and 
on foods depends on the reaction (alkalinity is 
favorable), and on the presence or absence of 
moisture. It lives longer in sterilized milk (ten 
days) than in that which contains other micro-or- 
ganisms. 
infection Infection develops in the small intestines fol- 
Dissemina- lowing ingestion of the organisms. Infection by 
way of the lungs or through wounds does not take 
place. In the patient the living vibrio occurs only 
in the intestines, and it is excreted only with the 
feces. So far as known, it has no normal habitat 
outside the body, although a stream or other water 
supply may contain the vibrio over a long period 
through constant reinfection of the water. This 
can only occur, directly or indirectly, through the 
stools of patients. The washing of soiled linen or 
bathing in water which is used for drinking and 
other household purposes have caused outbreaks of 
cholera. The water supply of a city may be in- 
fected by the discharges of patients who are con- 
fined to a ship. Convalescents may retain virulent 
organisms in their stools for forty-eight days 
(Kolle), and, as stated, healthy persons who are 
insusceptible to cholera and who have resided in 
an infected district may carry virulent vibrios in 
their intestines. These conditions have contrib- 
uted to the futility which, to a large degree, has 






DISSEMINATION. 473 

met attempts to limit the extension of cholera by 
quarantine measures. Cholera extends from conn- 
try to country along the lines of travel. In some 
instances it has been possible to trace the origin 
of widespread epidemics to the delta of the Ganges, Epidemics 
a region in which the disease is endemic. Pilgrims 
from India carry the infection to Mecca, and pil- 
grims from Egypt carry it to their native land on 
their return from Mecca. Either from Egypt, or 
through Arabia, Asia Minor and Southern Eussia 
or Turkey, cholera has, with more or less rapidity, 
extended to Western Europe. The development of 
rapid transit has increased the rapidity with which 
cholera may extend. From Europe the disease has 
been carried to various ports of the western conti- 
nent, Canada, the West Indies and southern ports 
of the United States, from which extension has oc- 
curred to different sections. Of six widespread 
epidemics of the past one hundred years, three 
have involved the United States, reaching consid- 
erable proportions. The means of introduction is 
not always apparent. 

As in typhoid, two types of epidemics are known, 
the two often being associated: First, that caused 
by water infection, and, second, that in which the 
disease spreads by direct and indirect contact. The 
explosive character of an epidemic caused by in- 
fection of a water supply is much more striking 
than in the case of typhoid fever. In large cities 
hundreds, or thousands, may be striken within a 
day. The brief incubation period, from twelve to 
twenty-four hours, contributes to the acuteness of 
the outbreak. The distribution of a "water- 
borne" epidemic corresponds with the distribution 
of the infected water. A remarkable occurrence il- 



474 INFECTION AND IMMUNITY. 

lustrating this point was noted in the epidemic 
which attacked Hamburg in 1892. In certain 
streets in which the residents of the two sides ob- 
tained their water supply from different sources, 
one of which was infected, cholera was limited to 
that side which was supplied with infected water. 
Only irregular cases due to contact infection oc- 
curred on the opposite side of the street. 

Epidemics which are due solely to contact infec- 
tion develop slowly and irregularly. A common 
incident is the successive involvement of the mem- 
bers of a family, whereas others in the immediate 
neighborhood are unaffected. Water-borne epi- 
demics are invariably complicated by the occur- 
rence of contact infection. The methods of con- 
tact infection are not different from those men- 
tioned under typhoid fever. Food or milk which 
has been infected by contaminated water or by 
other means may cause the development of isolated 
groups or cases. 
suscepti- Animals do not contract cholera under natural 
Animals, conditions. By rendering the gastric contents of 
guinea-pigs alkaline and introducing cultures into 
the stomach through a tube, Koch induced a chol- 
era-like process from which the animals died with- 
in from twenty-four to thirty-six hours; an intra- 
peritoneal injection of opium, to quiet peristalsis, 
seemed to be necessary for the success of the ex- 
periment. Similar results were obtained in very 
young rabbits by feeding cultures to them (Issaeff 
and Kolle, Metchnikoff). Guinea-pigs withstand 
the subcutaneous inoculation of moderate amounts, 
but are very susceptible to intraperitoneal inocula- 
tion. Intravenous injections are exceedingly toxic 
for rabbits, and a fatal cholera-like condition with 



CHOLERA ENDOTOXIN. 475 

localization of the organisms in the intestines and 
intestinal mucosa has been produced in this way 
(Thomas). 

The essential poison of the cholera vibrio is in- Endotoxin. 
tracellular, and becomes free only after solution of 
the bacterial cells. Cultures which are killed care- 
fully as by chloroform vapor (Pfeiffer) are highly 
toxic, although the fluid alone is non-toxic. The 
nitrates of young cultures have little or no poison- 
ous action. The toxicity of older filtrates is due 
partly to the solution of the bacteria with conse- 
quent liberation of endotoxin, and perhaps also to 
secondary disintegration products which have a 
certain toxicity. The soluble toxin of Metchni- 
koff, Koux, and Taurelli-Salimbeni is a dissolved 
endotoxin and not a secretion of the living cells, 
according to Kolle. 

Koch considers that cholera is an acute infec- conditions 

in the 

tious process of the intestinal epithelium, whereas intestines. 
the general condition is one of acute intoxication. 
It is assumed that the condition in the intestines 
corresponds to that in the culture media, i. e., that 
here, too, no true soluble toxin, comparable with 
that of diphtheria or tetanus, is secreted, but that 
the toxin which eventually reaches the circulation 
is that which is liberated from the bacteria after 
the latter have been dissolved by the bacteriolysin 
of the plasma, or perhaps by the leucocytes. Doubt- 
less a great deal of endotoxin is liberated in the in- 
testinal canal, but it is Koch's conception (cited 
by Kolle) that the primary intoxication comes 
from those organisms which have penetrated be- 
tween and beneath the epithelial cells and here 
have undergone solution. One effect of the toxin 
in this situation is to cause desquamation of the 



470 INFECTION AND IMMUNITY. 

intestinal epithelium, as a consequence of which 
rapid absorption of the toxin from the intestinal 
canal takes place through the denuded surface. 
This theory supposes that the toxin is not readily 
absorbed through the intact epithelium. The liv- 
ing vibrio has never been cultivated from the 
blood. 

The changes in the intestines depend on the 
duration of the infection. In cases which prove 
fatal within a few hours the mucosa shows only 
moderate general reddening, which is intensified 
at the borders of Peyer's patches and the solitary 
follicles. The intestinal contents are of^ a rather 
clear fluid nature in which are suspended flakes of 
mucus and epithelium; the fluid may be tinged 
with blood. With a longer duration the destructive 
processes in the mucosa become more intense, and 
consist largely of desquamation of the superficial 
epithelium and intense congestion of the denuded 
submucosa. In the more prolonged cases, "chol- 
era-typhoid," the mucosa, especially above the ileo- 
cecal valve, may show diphtheritic necrosis. The 
serous surface of the intestines is injected. 
Prophylaxis. The rational prophylaxis founded by Koch, on 
a knowledge of the biologic characteristics of the 
comma bacillus, has proved of great efficiency. 
The essential points are the following: 1. Imme- 
diate bacteriologic examination of the stools in 
suspicious cases. 2. Absolute isolation of patients, 
in a hospital whenever possible. 3. Thorough dis- 
infection of the stools, linen, room and all articles 
with which the patient has been in contact, includ- 
ing water-closets and privies. 4. Continued iso- 
lation during convalescence until the stools are 
free from vibrios. 5. Eepeated bacteriologic ex- 



PROPHYLAXIS. All 

animation of the stools of those who have been in 
contact with cholera patients until their freedom 
from vibrios is assured. 6. Frequent examination 
of the water supply at different points in order to 
detect the occurrence of water infection. 7. In 
case water infection exists, exclusion of the water 
from all domestic uses, and the institution of 
means to rid the water of infection. This may be 
done in the case of infected wells, but in the case 
of large systems reconstruction may be necessary 
for future protection. Water for household use 
should be boiled. Kolle compares the conditions 
in Germany and Russia during the epidemic of 
1892-4. In Germany, where Koch's principles of 
prophylaxis were rigidly observed, about 10,000 
cases occurred, 9,000 of which were confined to 
Hamburg, whereas in Russia, where precautions 
were not enforced strictly or generally, 800,000 
cases developed during the same period. 

Protective inoculation has shown itself to be of vaccination. 
distinct value for prophylaxis. Ferran, a Span- 
iard, first practiced vaccination on a large scale in 
1884, although little definite knowledge of the 
value of the procedure resulted from his work. 
He is supposed to have used impure cultures. Haff- 
kine introduced protective inoculation on a large 
scale in India, and up to 1895 had inoculated 40,- 
000 persons. Following Pasteur's method with 
anthrax, he used two vaccines. Vaccine 1 was a 
culture which had been attenuated by prolonged 
growth at 39° C. Vaccine 2, which* was adminis- 
tered five days later, was a virulent culture. The 
living organisms were used in both vaccines and 
the injections were given subcutaneously. The 
local and general symptoms were mild. Instead 



478 INFECTION AND IMMUNITY. 

of living cultures Kolle has proposed the use of 
virulent cultures which have been killed by expo- 
sure to a temperature of 58° C. for one hour. The 
vaccine is preserved by the addition of 0.5 per 
cent, phenol. In the Japanese epidemic of 1902 
this method was used on an extensive scale. The 
incidence of disease among the uninoculated was 
13 per cent., among the inoculated 0.06 per cent. ; 
the mortality among the uninoculated was 10 per 
cent., among the inoculated only 0.02 per cent. 
The disease, when it occurred in the inoculated, 
was of a mild type. A single injection of from 2 
to 4 mg. of a killed agar growth was given sub- 
cutaneously (cited by Kolle). Strong has pro- 
posed the use of the products of autolysis of the 
cholera vibrio as a vaccinating substance, a method 
founded on the observations of Neisser and Shiga 
in relation to typhoid, and of Conradi and Drigal- 
ski in relation to dysentery. The local and general 
symptoms are said to be of a mild type. The 
method has had no practical trial. 
Natural From what was said above in connection with 
and suscep- the so-called cholera carriers, it is evident that not 
all are equally susceptible to infection with chol- 
era. In the few instances in which infection has 
been attempted deliberately, some contracted the 
disease, at least one case ending fatally, whereas in 
others either a mild infection or none at all took 
place. The conditions on which such cases of in- 
dividual immunity depend are not known conclu- 
sively, although it is often intimated in a general 
way that a strong bactericidal power of the body 
fluids, or a high phagocytic power on the part of 
leucocytes, is responsible for it. The gastric juice, 
on account of its acidity, offers a barrier to the 






tibility. 



IMMUNITY IN CHOLERA. 479 

passage of living vibrios into the small intes- 
tines, and this is particularly true of cholera. 
It is nevertheless evident that the barrier in many 
instances is not a serious one. A number of cases 
are recorded in which investigators while working 
with cultures have become infected with cholera, 
the cases running typical courses which sometimes 
ended fatally (Pfeiffer, Pfuhl and others). Or- 
ganisms which are ingested with water may pass 
rapidly to the intestines without being affected by 
the acid of the stomach, or when taken with food 
they may be buried in the latter and hence not 
come in contact with the gastric secretion. It 
seems probable that the intestinal epithelium has 
a certain resistance to invasion which is most mani- 
fest in the case of those who do not become in- 
fected in spite of the presence of the organisms in 
their intestines. Natural immunity appears to be 
one which is directed against the bacteria rather 
than against the endotoxin, proliferation of the 
organisms in the intestinal epithelium being pre- 
vented. Poorly nourished individuals, the very 
young and the very old are particularly suscepti- 
ble. Other gastrointestinal disorders, in the pres- 
ence of an epidemic, predispose to infection. De- 
fects in the intestinal epithelium, or a decreased 
resistance of the latter, may afford favorable 
conditions for invasion. 

Active immunity, as that which results from in- Acquired 
fection or from protective inoculation, is charac- mm,mi : 
terized by the appearance of bactericidal ambocep- 
tors, opsonins, agglutinins and specific precipitins 
in the serum. 

Amako finds that opsonin, bactericidin and 
agglutinin develop with the course of the disease. 



480 INFECTION AND IMMUNITY. 

The length of the negative phase varies with the 
severity of the symptoms. The fulminating cases 
have a short negative phase ending in death. The 
antibodies reach their height during convalescence, 
the bacteriolysins usually developing most rapidly. 
In most cases the three antibody curves run 
parallel, but the bacteriolysins may be much more 
highly developed than the opsonins. 

According to Pfeiffer and Marx, the antibodies 
are produced in the blood-forming organs. An 
attack of cholera confers immunity of prolonged 
duration, although it is not always absolute. 

Passive immunity is readily induced in animals 
by injection of anticholera serum. As in other 
instances, it is of short duration. Doubtless the 
same condition may be induced in man. Besredka 
has proposed mixed immunization for protective 
inoculation, using killed bacteria which have been 
saturated with the specific amboceptors. 
.serotherapy Serotherapy has been no more successful in 

and Agglnti- 

nation, cholera than in typhoid fever. The antitoxic 
serum of Eoux and others has had no practical 
trial. According to Achard and Bensaude, the 
serum of cholera patients, on the third or fourth 
day of the disease, agglutinates the cholera vibrio. 
However, they used the serum in dilutions of 1-20, 
and in this strength even normal human serum 
may be agglutinating (Pfeiffer and Kolle, cited by 
Paltauf). Convalescents even after seven months 
may show an agglutinating power of from 1/100 to 
1/120. 

The bacteriologic examination of the stools is 
the most reliable means of early diagnosis (see 
above). 



BACILLUS PESTIS. 481 

VII. PLAGUE. 

Plague was known in the second and third cen- 
turies. In the sixth century it ravaged the Roman 
empire and destroyed half the population in the 
eastern provinces. Under the name of the "black 
death" it swept over Europe in 1347-50 with a 
sacrifice of one-fourth of the inhabitants — about 
25,000,000. During the fifteenth and sixteenth 
centuries many epidemics prevailed in various 
parts of Europe, and the disease seemed to have 
fastened itself on that part of the world. However, 
the pneumonic form of the disease, the most con- 
tagious, gradually became less common, or the vir- 
ulence of the infection diminished, and this, with 
the institution of quarantine regulations, decreased 
the prevalence of the plague during and following 
the seventeenth century. Nevertheless, there have 
been occasional outbreaks in Eastern Europe since 
that time. Following the recrudescence of plague 
in Hongkong in 1893 and in other places later, 
the disease has been subjected to scientific study, 
its cause has been discovered, and the importance 
of rigid quarantine measures at seaports in pre- 
venting its universal extension has been proved. 

In the Hongkong epidemic of 1893-4 Kitasato 5? i ^J ra < J *® rls - 
and Yersin, working independently, discovered the organism. 
bacillus of plague, Bacillus pestis. The organism is 
minute (1.5 to 1.75 by 0.5 to 0.7 microns), and 
typically is of long oval shape. The frequent oc- 
currence of short oval cells (coccus form), longer 
rods and distorted, swollen, vacuole-like cells (in- 
volution or degeneration forms) signifies a high 
degree of pleomorphism which is characteristic. 
The longer the disease has lasted, or, on the other 
hand, the older the culture, the more numerous are 



482 INFECTION AND IMMUNITY. 

the atypical forms. In bouillon long chains de- 
velop. It is non-motile, has no flagella and forms 
no spores. A capsule may be demonstrated by ap- 
propriate technic. It does not stain by Gram's 
method, and with methylene blue, carbol fuchsin, 
etc., the ends stain more densely than the central 
portion (polar staining). Because of its general 
properties it is placed in a group with a number of 
bacteria which cause . hemorrhagic septicemias in 
various animals — the "hemorrhagic septicemia 
group." 

There occurs in bouillon the so-called stalactite 
growth, in which visible processes extend from the 
surface toward the bottom, where they meet other 
processes which extend toward the surface "stalag- 
mites"). These formations utilize as their starting 
points the side of the flask or drops of butter or 
oil which are placed on the surface. Certain other 
organisms grow in a similar manner. It is said 
to be a characteristic feature of the plague bacilli 
that many involution forms appear on agar which 
contains 3 per cent, of sodium chlorid. The opti- 
mum temperature for growth is from 25° to 30° 
C, which is somewhat lower than that for most 
pathogenic organisms. It grows rather slowly even 
under the best conditions. In mixed cultures it is 
overgrown by saproplrytie organisms (e. g., colon 
bacillus). 
viability Tn e plague bacillus may live for from four to 
Resistance, seven days in the putrefying organs of man or ani- 
mals. Its virulence may be retained in the cadaver 
of a rat for two months (Bandi and Stagnitta- 
Balistreri) . During this time the organisms pene- 
trate all the tissues of the body, even growing 
through the skin. It may live in the pus of a 



BACILLUS PESTIS. 483 

bubo for twenty days when unmixed with other 
organisms (Albrecht and Ghon) ; in the sputum 
from plague pneumonia for ten days; in various 
foods, as milk, potatoes, for one to three weeks ; in 
water from five to twenty days, depending on the 
number of saprophytes which are present; in earth 
from two weeks to three months, depending on the 
quantity of organic matter and other organisms. 
In all these instances the higher the temperature, 
i. e., above 30° C, and the more numerous the 
saprophytic organisms, the shorter is the life of 
the plague bacillus. In winter, when contaminat- 
ing saprophytes grow less rapidly, the plague bacil- 
lus lives longer. Its resistance to desiccation, sun- 
light and disinfecting agents is rather low, par- 
ticularly when the surrounding temperature is 
above 30° C. In temperatures of from 29° to 31° 
C, when thorouhgly dried, it rarely lives longer 
than from six to seven days, whereas at lower tem- 
peratures, 16° to 20° C, cultures may be obtained 
after from one to several weeks, depending on the 
material which contains the organisms. It lives 
longer in woolen and cotton threads (clothing) 
than when isolated as in dust ; hence, dust infection 
is improbable (Dieudonne). In sputum (plague 
pneumonia) and purulent exudates in which the 
bacilli become incrusted to a degree, life may per- 
sist for from three to four weeks. Sunlight kills 
them in from two to six hours, depending on the 
temperature and the proximity of the organisms to 
the surface. Although cultures for the purpose of 
vaccination have been killed at a temperature of 
65° C. for one hour, precautions to insure an even 
distribution of the heat are necessary to render cer^ 
tain the death of all organisms. A temperature of 






aad Toxins. 



484 INFECTION AND IMMUNITY. 

100° C. kills them at once, and 80° C. in from five 
to ten minutes (moist heat) . They are very resis- 
tant to cold, remaining alive at a temperature of 
— 20° C. for several weeks, even when repeatedly 
thawed out during this time, and they even prolif- 
erate slowly at from 4° to 7° C. 
virulence Cultures of the plague bacillus retain their viru- 
lence over a long period when kept in a cool dark 
place and when not allowed to dry. However, 
they often loose in virulence unaccountably. The 
nature of the toxic substance is as yet obscure. A 
concentrated soluble toxin has never been obtained 
in cultures. Filtrates of young cultures show lit- 
tle or no toxicity, whereas in older cultures the 
fluid becomes more or less toxic (liberation of en- 
dotoxin?). Lustig and Galeotti extract cultures 
with 0.75 to 1 per cent, potassium hydroxid, from 
which they precipitate a toxic substance with ace- 
tic or hydrochloric acid. Markl found the cell 
bodies to be very toxic after eight weeks' growth at 
room temperature, provided the organisms were 
killed by chloroform rather than by heat: killing 
by heat destroys the toxic substance largely. He 
believes some metabolic product of the organism 
is the chief toxic constituent, claiming at the same 
time the presence of a certain amount of soluble 
toxin. 

The plague bacillus is exceedingly virulent for 
rats, squirrels, guinea-pigs and monkeys ; somewhat 
less virulent for mice and adult rabbits ; other ani- 
mals, cats, dogs, swine, cows, horses, sheep, goats, 
may be infected artificially, although they com- 
monly recover even after large doses. Guinea-pigs 
and rats may be infected by subcutaneous, intraperi- 
toneal and intravascular injections, by the feeding 



Virulence 

for Animals. 



TRANSMISSION TO ANIMALS. 485 

of infected material or by placing it on the nasal 
mucous membrane or in the conjunctival sac, and by 
inhalation experiments, the last method commonly 
resulting in plague pneumonia. Guinea-pigs and 
young rabbits die of plague septicemia in from 
four to five days when cultures or material con- 
taining the organisms (sputum, feces, organs from 
plague cases), are rubbed into the shaven or even 
unshaven skin (Albrecht and Ghon). This experi- 
ment is of value for detecting virulent plague ba- 
cilli and separating them from contaminating or- 
ganisms. Following inoculation into a cutaneous 
or mucous surface a local reaction of varying in- 
tensity develops in which the subcutaneous tissue 
becomes edematous or even hemorrhagic, in a num- 
ber of hours the regional lymph glands become 
swollen and hemorrhagic, and in from two to five 
days the. animals die of plague septicemia. Cul- 
tures of low virulence not infrequently cause a 
chronic infection which is characterized by the for- 
mation of large granulomatous nodules on the sur- 
face of the liver and spleen and in the omentum. 
Such foci contain many plague bacilli, and the 
death of the animal results in a few weeks from 
intoxication or from general infection. Although 
rabbits are much less susceptible than rats or 
guinea-pigs, young animals succumb to cutaneous 
inoculation. 

Dieudonne cites four foci in which plague is Endemic 
known to be endemic at the present time : One is 
in China (province of Yunnan), from which the 
Hongkong epidemic originated ; a second in the 
Himalayas, which led to the outbreak in Bombay; 
a third in a mountainous region south of Mecca, 
and a fourth was found by Koch and Zupitza in 



Plague. 



480 INFECTION AND IMMUNITY. 

British East Africa near the source of the White 
Nile. 
Plague The opinion is held by many that plague is pri- 
n squu-reT^! marily a disease of the rat and that certain regions 
remain pest-infected because of this fact. Eats, in 
certain districts, surfer from a chronic form of the 
disease, and it is possible that the organism at 
times acquires increased virulence, as a conse- 
quence of which the infection becomes widespread 
and rapidly fatal among these animals. It is 
believed that transmission from rat to rat may 
occur through the eating of plague cadavers. 
Experiments are also reported showing that fleas 
from plague-stricken rats will infect healthy rats, 
guinea-pigs and monkeys by biting them. The 
work of the Indian Plague Commission demon- 
strated that the usual means of transmission from 
rat to rat and from rat to man is by means of 
fleas. Monkeys, which are readily infected if put 
in the same room with infected rats, remain well 
if protected from fleas. It has been repeatedly 
demonstrated that fleas from rats and squirrels 
will feed on man. 

In California, squirrels infected with plague are 
an important source of infection in man. Trans- 
mission from rats to squirrels and from squirrels 
to rats by means of fleas has been demonstrated by 
McCoy, and McCoy and Wherry report a case of 
transmission from squirrels to man, probably 
through fleas. 

Flies, as well as fleas, may distribute the bacilli 
from rats or the infected excretions of man 
mechanically. 

When plague invades a new country it commonly 
makes its first appearance in coast cities. Pre- 



TRANSMISSION OF PLAGUE. 487 

sumably this is accomplished through infected rats 
which may board a ship during its stay in a pest- 
ridden harbor, and which subsequently escape at 
the new port. 

Epidemics of plague lack the explosive-like sud- Epidemics. 
denness in their development which characterize3 
cholera and, to a certain extent, typhoid and dys- 
entery. The cases occur in groups and in particu- 
lar houses in such a manner that direct and indi- 
rect contact seem to be largely responsible for 
transmission. Every epidemic of plague may be 
divided into three stages : a slow progression from 
small centers, an acme of widespread death, and a 
slow recession (Dieudonne). It seems probable 
that the disease spreads rapidly and extensively 
only when the pneumonic form prevails. 

In man infection takes place through the skin ^J' j£ tiom 
most frequently, although the mucous membranes 
of the mouth, nose, pharynx, tonsils or the con- 
junctiva are possible infection atria. Often no 
local reaction is produced, and the point of en- 
trance may be indicated only in a general way by 
the swollen lymph glands of the region. Infre- 
quently a pustule or small carbuncle marks the 
point of entrance. Primary plague pneumonia is 
caused by the inhalation of pest-laden material, 
particularly fine particles of sputum from a pneu- 
monic case, and perhaps also by the inhalation of 
infected dust; the latter is probably of less impor- 
tance because of the short life of the organism in 
dust. Even in ordinary speaking minute drops of 
saliva are thrown into the air. Infection is thought 
not to occur through the stomach or intestines. 
In the pneumonic and septicemic forms, the in- 
fected urine and feces contribute to the dissemina- 






488 INFECTION AND IMMUNITY. 

tion of the organisms. Compared with pneumonic 
and septicemic plague the bubonic form is much 
less dangerous to a community. 

Following cutaneous infection the regional 
lymph glands become swollen and hemorrhagic, 
and undergo more or less extensive necrosis. When 
the infection extends beyond the lymph glands the 
blood may contain enormous quantities of bacilli 
(plague septicemia), and the same condition fol- 
lows plague pneumonia ; in the event of general in- 
fection death follows in a few hours. "Secondary 
pneumonia" and also "secondary buboes" develop 
as a consequence of blood infection. Hemorrhages 
into the mucous membrane (especially the stom- 
ach or cecum), endothelial surfaces (pericardium), 
and various parenchymatous organs, with extreme 
degeneration of the latter (liver, kidneys and 
heart), are characteristic anatomic changes. The 
spleen is usually swollen. The toxic substance 
evidently has affinities for many tissues. 

Mixed infection with the streptococcus is not 
uncommon and is a serious complication. 
prophylaxis. The following are important points for prophy- 
laxis: 1. Early diagnosis as established by bac- 
teriologic examination of blood, sputum, and fluid 
taken from a bubo either by a syringe or after in- 
cision ; 2, in the thorough isolation of patients and 
of those who have been exposed to infection; 3, 
in the disinfection of excretions, of clothing and of 
infected houses, which in some instances may 
mean the destruction of the latter; 4, in the de- 
struction of rats; 5, prophylactic injections. Up 
to the present time the most effective measure of 
getting rid of rats is to offer a bounty for each 
animal caught, as practiced in Manila. In Cali- 



PROPHYLAXIS. 489 

fornia, the work of extermination of squirrels, rats 
and fleas has been carried on extensively by the 
U. S. Public Health and Marine-Hospital Service. 

The vaccine of Haffkine has been used exten- 
sively in India. The Indian plague commission 
found that the incidence of disease and the mor- 
tality were lower among the inoculated than the 
uninoculated, although many of the inoculated 
contracted the disease in a benign form. The vac- 
cine consists of bouillon cultures which have grown 
for six weeks with stalactite formation (see above), 
then killed by exposure to a temperature of 65° C. 
for one hour; from 0.5 to 3.5 c.c. are injected, ac- 
cording to the age and size of the individual. One 
or more subsequent injections may be given. The 
local and general reactions are of moderate sever- 
ity. Protection becomes manifest only several 
days after the inoculation and may persist for 
many weeks or months. The vaccine recommended 
by the German commission consists of two days' 
old agar cultures which have been killed by heat 
(65° C. for one hour). Lustig and Galeotti utilize 
the toxic precipitate described above as a vaccine. 
Terni and Bandi inoculate rabbits or guinea-pigs 
intraperitoneally with the plague bacillus and 
after or just preceding death collect the peritoneal 
exudate, in which the organisms are allowed to pro- 
liferate still further for twelve hours. The bacilli 
are then killed at a low temperature, and this 
fluid, after an addition of a preservative, consti- 
tutes their vaccine. Although the last three vac- 
cines have proved of value in animal experiments, 
they have not as yet been used extensively in man. 

Besredka and Shiga recommend the use of mixed 
active and passive immunization, as suggested in 



490 INFECTION AND IMMUNITY. 

relation to typhoid and cholera, in this instance 
naturally using plague bacilli (killed) and anti- 
plague serum. Shiga reported good results by the 
use of the combined method in the epidemic in 
Kobe. 

The immunity which is produced by protective 
inoculation, like that which follows natural infec- 
tion, is considered to be antibacterial inasmuch as 
the serum acquires increased bactericidal power for 
the bacillus, but shows no ability to neutralize its 
toxic constituents. The influence of opsonins is 
essential for experimental phagocytosis, and is an 
important factor in the mechanism of immunity. 
Antiplague serum contains also complement-devi- 
ation antibodies and precipitins. The immunity 
which follows infection is of long duration. 
serotherapy Prophylactic injections of antiplague serum pro- 
duce a temporary immunity of about two weeks' 
duration. The Pasteur Institute prepares the 
serum of Yersin by immunizing horses first with 
killed and then with living cultures. The immun- 
ization is difficult and from several months to a 
year and a half are required for the production of 
a strong serum. When the blood is drawn its free- 
dom from living plague bacilli and from toxic sub- 
stances must be assured. The immunizing value of 
the serum is determined by that quantity which 
will save a mouse from a fatal dose of living plague 
bacilli, the serum being given 24 hours in advance 
of the culture. This is accomplished by 0.1 to 0.02 
c.c., depending on the strength of the serum. Its 
curative power is estimated from that quantity, 0.5 
to 0.1 c.c, which saves a mouse when administered 
16 hours after the injection of an otherwise fatal 
dose of culture. For protective inoculation in man 



and Prophy- 
laxis. 



SEROTHERAPY. 491 

from 10 to 20 c.c. are recommended, and for cura- 
tive purposes from 30 to 50 c.c. Concerning the 
value of this serum Dieudonne concludes as fol- 
lows: "On the basis of the results obtained in 
man and in animal experiments we can attribute 
no positive curative value to the Parisian serum, 
although a certain influence on the course of the 
disease can not be denied. On the other hand, the 
serum is suitable for protective inoculation when 
immediate immunity is necessary, as for those who 
are caring for cases of plague pneumonia. Since, 
however, the protection afforded by this means per- 
sists only for a few days, subsequent active immun- 
ization with killed cultures is indicated as soon as 
possible for those persons who are exposed to in- 
fection for some time." The favorable results 
noted by a number of observers would seem to jus- 
tify further use of the serum for curative pur- 
poses. 

The serum of Tavel, prepared at the Institute 
of Bern, is, like that of Yersin, bactericidal and 
agglutinating. Antitoxic as well as bactericidal 
properties are claimed for the serum of Lustig, 
which is prepared by immunization with the toxic 
precipitate mentioned above. It has been used ex- 
tensively in the treatment of plague and in a num- 
ber of small epidemics favorable though not thor- 
oughly convincing results were reported. The 
serum of Markl, which is supposed to be antitoxic, 
has had no practical trial. It is prepared by im- 
munization with old cultures which have been 
killed by chloroform. 

According to Kolle and Krumbein antiplague 
serum should be tested as to concentration of all of 



492 INFECTION AND IMMUNITY. 

the various antibodies in order to obtain a correct 
idea of its value. 
Ag-g-inti- Although the serum of patients acquires a cer- 
tain agglutinating power, it is rather low (1/3 or 
1/5), and does not become manifest until during 
the second week of the disease. Before this time 
diagnosis by clinical or bacteriologic means can be 
made with certainty; hence, for clinical diagnosis 
the reaction has little value. On the other hand, 
a strong artificial agglutinating serum obtained 
by the specific immunization of animals is of great 
value for the identification of the plague bacillus 
when cultures have been obtained from suspected 
cases. Artificial serums may agglutinate in dilu- 
tions of from 1/1000 to 1/6000." 

B. Diseases in which acquired immunity is not 
clue to increased bactericidal power of the serum, or 
lenowledge on tliis point is deficient. 

I. ANTHRAX. 

From the standpoint of infection and immunity 
anthrax is of particular interest. It is the first 
disease of which the bacterial etiology was proved 
and in which the specific microbe was used in pure 
culture for the production of artificial immunity 
(vaccination). 

Anthrax is particularly a disease of cattle and 
sheep, and it prevails in certain European coun- 
tries, especially Eussia, in Australia and in South 
America. It does not occur extensively in this 
country. Definite regions are at times heavily in- 
fected, and it is in such localities that the disease 
is most frequently transmitted to man. 



ANTHRAX. 403 

As earh' as 1850 Kayer and Devaine, also Pol- Bacillus 
lender, had discovered the presence of small rods 
and filaments in the blood of animals which had 
died of anthrax, and the work of Koch, Pasteur 
and others soon established that this rod, the an- 
thrax bacillus, is the cause of anthrax. The discov- 
ery of Koch that the bacillus forms extremely re- 
sistant spores, explained the persistence with which 
the disease infects particular localities. 

The anthrax bacillus is a fairly large organism, spores. 
is rod-shaped, non-motile and grows with charac- 
teristic appearances on various culture media. 
With the proper temperature and culture medium, 
and in the presence of free oxygen, the formation 
of spores begins after about twenty-four hours of 
growth. Their evolution is complete in from one 
to two days, and eventually the protoplasm of the 
cells disintegrates and the spores are set free. 
Spores are not formed in the body of an infected 
animal. Spore formation is not essential, how- 
ever, for the continued life of the organism; at 
high temperatures (42° C), and in the presence 
of minute amounts of acids and alkalis or of car- 
bolic acid, strains may be so altered that they lose 
permanently the ability to produce spores. Under 
favorable conditions the spores germinate com- 
pletely in from three-quarters to one and one-half 
hours (Grethe) by a process in which they lose 
their refractive appearance and assume first an 
oval and then a rod shape. In the body a capsule 
surrounds the bacillus, and it grows singly or in 
very short chains ; in culture media it is very diffi- 
cult to obtain capsules. The long threads which 
appear in culture media, especially bouillon, are 
not found in infected animals. 



494 INFECTION AND IMMUNITY. 

Resistance The bacillus itself shows no unusual resistance, 
lence. but its spores are more resistant than those of any 
other pathogenic bacterium. When dried on a 
thread they have been known to live for from ten 
to twelve years. Corrosive sublimate (1-2000) 
kills them in forty minutes (Fraenkel), and direct 
sunlight in about 100 hours (Momont). Bacillus 
pyocyaneus, streptococci, staphylococci and the ba- 
cillus of Friedlander are said to antagonize its 
growth, and Eettger found that the dried B. prodi- 
giosus decreased the virulence of the organism for 
animals when the two were injected. 

The anthrax bacillus is remarkable for its infec- 
tiousness. A twenty-millionth of a loop of a viru- 
lent culture will cause a fatal infection in mice, 
guinea-pigs and rabbits, when given subcutaneous- 
ly. A systemic infection may be produced by feed- 
ing the spores or causing animals to inhale them. 
The gastric juice is able to kill the bacilli, but not 
the spores, which germinate after they reach the 
intestines. 

The organism is distributed by the excretions 
of diseased animals, and after their death the ad- 
jacent soil becomes heavily infected by the dis- 
charges which escape from the intestines and blad- 
der. In this situation the bacilli pass into the 
sporing stage, in which they remain viable and 
virulent for a long time. 
infection The infection of herds usually is accomplished 
by the ingestion of spores which have been distrib- 
uted in this way, the spores germinating, as de- 
scribed above, after they have reached the intes- 
tines. The disease may be primary in the skin in 
the form of malignant pustule. In man malignant 
pustule is the commonest type of infection, occur- 



Atria. 



ANTHRAX. 



495 



ring especially among those who have to do with 
cattle and sheep. The bacilli, however, may gain 
entrance through the lungs as in the so-called 
"wool-sorter's" disease, which is caused by the in- 
halation of infected dust from the raw material. 

The generalized infection in all animals is rapid- 
ly fatal (one to three days), and the occurrence of 
death is sometimes so sudden as to be called apo- 
plectiform; in man the mortality is about 50 per 
cent. Malignant pustule runs a more favorable 
course. 

The general infections are marked by symptoms Toxin. 
of intense intoxication and acute degenerative 
changes are produced in the parenchymatous or- 
gans. Massive numbers of the bacilli are found in 
the blood. Neither a soluble toxin nor an endo- 
toxin characteristic for the organism has been dem- 
onstrated up to the present time (Sobernheim), 
although there is abundant clinical and anatomic 
evidence of intense intoxication. The production 
of mechanical injuries by the large masses of ba- 
cilli in the circulation is doubtful. 

Eational prophylaxis involves the proper dispo- Prophylaxis. 
sal of the bodies of animals which have died of ■ 
anthrax, the exclusion of animals from fields 
known to be infected, suitable disinfection of stalls, 
and finally protective inoculation against the dis- 
ease. No part of the anthrax cadaver should be 
used for commercial purposes, because of the dan- 
ger of infecting those who work with the raw ma- 
terials. Cleanliness and the usual precautions 
against contagious diseases should be observed by 
those who are exposed to infection, bearing in mind 
that the disease may be transmitted by way of the 
lungs and alimentary tract, as well as by the skin. 



496 INFECTION AND IMMUNITY. 

Natural im- It is probable that no disease is more perplexing 
"^SuiceptY- from the standpoint of immunity than anthrax. 
biiity. rpj ie var i a tions in susceptibility and immunity 
among different animals are extreme: Guinea- 
pigs, rabbits and mice are probably more suscepti- 
ble than sheep and cattle ; compared with these the 
dog and rat are relatively immune, whereas fowls 
and cold-blooded animals can be infected with dif- 
ficulty. Although the microbe is readily killed by 
suitable serums (rabbit, e. g.), such an effect is not 
an index of immunity. The serum of the highly 
susceptible rabbit is strongly bactericidal in test- 
glass experiments, whereas that of the more resist- 
ant dog, or rat, has little or no bactericidal power. 
Because of this inconsistent relationship of the 
serum to immunity, and since the leucocytes have 
a high phagocytic power for the anthrax bacillus, 
Ptruschky, Frank and others agree with Metchni- 
koff in assigning variations in the natural immun- 
ity of different animals to variations in phago- 
cytic power. Bail and Pettersson, in extensive ex- 
perimental work, discovered conditions which, they 
believe, explain the lack of correspondence between 
serum properties and natural immunity. In the 
serum of the relatively immune dog and chicken 
they found bactericidal amboceptors but no com- 
plement; hence, the serum could show no bacteri- 
cidal action in the test-glass. If, however, leuco- 
cytes from the same animals were added to the 
serum, the latter became bactericidal. It may be 
assumed that in the course of infection the ambo- 
ceptors are activated by complement which is dis- 
charged from the leucocytes. The failure of the 
bactericidal substances of the rabbit's serum to 
protect the animal was ascribed to the ability of 






VACCINATION IN ANTHRAX. 497 

the tissues to absorb the amboceptors (Sobern- 
heim). Their work is of sufficient importance to 
demand repetition. 

Wright has shown the importance of the opsonins 
for phagocytosis of the anthrax bacillus. 

Eecovery from spontaneous infection is said to 
confer a degree of immunity, which, however, is 
not permanent. 

Artificial immunity may be produced by active vaccination. 
or passive immunization. The first attempts at 
vaccination were made in 1880 by Toussaint, who 
injected the blood of infected animals after it had 
been heated to 55 degrees for ten minutes. The 
bacilli were thus attenuated, but they were able to 
form spores subsequently and vaccination was not 
always successful. Pasteur used two vaccines. Vac- 
cine I consisted of a culture which was attenuated 
by growth at 42° C, and which contained no 
spores. Yaccine II was a virulent culture, and was 
injected in from ten to fourteen days after vac- 
cine I. Its use is said to have caused a decrease 
in anthrax in heavily infected districts, with a con- 
sequent decrease of the disease in man. Various 
modifications of the vaccines of Pasteur have been 
devised by others, and they seem to be equally suc- 
cessful. In some instances killed bacilli and the 
products of bacterial growth have been used with 
less success. The Anthracase-Immunproteidin of 
v. Emmerich and Lowe is not of established value. 

Immune serum for therapeutic purposes is pre- Ser 1 °p 1 l f ra ^ 
pared by immunization, first with killed or atten- laxis. 
uated cultures and then with virulent strains. The 
two vaccines of Pasteur may be used. Although 
the serum has been shown to have fairly strong 






498 INFECTION AND IMMUNITY. 

protective powers, it is of less value when used for 
curative purposes. It produces no effect after the 
blood stream has been invaded by the bacilli. Its 
greatest value is for the protection of herds when 
anthrax has declared itself. In man it has been 
used chiefly in the treatment of malignant pustule 
in which the prognosis, even without specific treat- 
ment, is not unfavorable. The best known serums 
are those of Sclavo, prepared from the goat and ass, 
of Mendez and Deutsch. The properties on which 
the value of the serums depends are unknown. So- 
bernheim is very positive in stating that the bac- 
tericidal power of an animal's serum is not in- 
creased by immunization or infection, and the ex- 
istence of an antitoxin is not recognized. As in 
some other instances immunization may cause an 
increase in opsonins which would render the serum 
effective by its power to cause increased phagocy- 
tosis. 
Mixed im- The method of Sobernheim, that of mixed active 
aiJd U Assiuti- an d passive immunization, seems to be successful 
atiou. as a prophylactic measure. The vaccine consists 
of a mixture of antiserum and bacilli. Immune 
and even normal serums at times may agglutinate 
the anthrax bacillus, but the reaction is inconstant, 
and the ability of an immune serum to cause ag- 
glutination is no index of its protective power. Ag- 
glutination is somewhat difficult of determination 
because of the tendency of the bacillus to grow in 
the form of chains. 

II. MALTA FEVER. 

Malta, Mediterranean or undulant fever, discovered 
in the Island of Malta, also occurs among British 
troops at Gibraltar, and cases have been discovered 



MALTA FEVER. 499 

in the Caribbean Sea, Porto Bico, in Hongkong, 
Manila, and in India. Historically, it has been 
traced to the beginning of the nineteenth century, 
but it was first described as an independent disease 
by Marsten in 1859. It is said to be extending. 
The disease usually runs a long course, which is 
somewhat typhoidal in character, and there may be 
one or more relapses. The spleen is enlarged, but 
the intestines are not involved. 

"It is distinguished from typhoid by its long du- 
ration, sometimes extending over many months; 
by a course of fever exhibiting marked undula- 
tions; by the occurrence of copious perspirations; 
by the frequent appearance of rheumatic articular 
disorders as well as by neuralgia and inflammation 
of the scrotum and epididymis" (Scheube). It 
occurs especially in the summer months. The 
incubation period is about fifteen days. 

Basset-Smith found the serum in practically all 
stages of the disease and in convalescence to have 
little or no bactericidal power for the coccus. Nor- 
mal serum appeared to be more bactericidal than 
that of the patients, although such an action was 
often missed in normal serum. Wright says that 
normal human serum is devoid of bactericidal 
power for the organism. Basset-Smith also con- 
cluded that the phagocytic power of the patient's 
leucocytes is less than in the case of normal leuco- 
cytes. According to Wright, the organism "is em- 
inently sensible to the opsonic action of the nor- 
mal serum," under the influence of which it is 
taken up in large numbers by the leucocytes. 

Agglutination by the serums of patients takes 
place in dilutions varying from 1-300 to 1-2000 






500 INFECTION AND IMMUNITY. 

or even as high as 1-6000. Agglutinins develop 
fairly early in the course of the infection, and the 
test is of great diagnostic importance. They dis- 
appear in about two years after recovery (Birt and 
Lamb ) . 

Bacillus melitensis, discovered by Bruce (1887) 
in the spleen of patients who had died of the dis- 
ease, is a minute organism, slightly oval in shape. 
According to Gordon, it possesses one flagellum, 
rarely two or four, and is slightly motile. The 
bacillus is found in pure cultures in the spleen, 
which is greatly enlarged. Its growth in culture 
media is very slow. 

It is thought that infected water may be one 
means of transmission of the disease. Laboratory 
infections with pure cultures have occurred 
through small wounds resulting in typical attacks 
of Malta fever (Birt and Lamb). The disease is 
not transmitted from person to person. 

Up to the present time the monkey is the only 
animal known with susceptibility to artificial infec- 
tion, although the organism has a certain viru- 
lence for rabbits and guinea-pigs on intraperito- 
neal or intracerebral injection (Durham). 

One attack confers immunity, which may disap- 
pear, however, after some time (Hughes). 

An immune serum which was prepared by 
Wright is said to influence favorably the course of 
the disease. 



CHAPTEK XXVI. 
GROUP III. 



Acute infectious diseases in which acquired im- 
munity of prolonged duration is not established. 
In some instances soluble toxins are produced 
which are of unknown importance in the infections 
(staphylococcus., streptococcus). Some of the or- 
ganisms contain rather strong endotoxins (pneu- 
mococcus, gonococcus), whereas in others a reason- 
able basis for their infectiousness is not at hand. 
In some instances immunization causes increased 
resistance to infection (staphylococcus, streptococ- 
cus), whereas this property has not been fully 
demonstrated in others. 1 The serums of immun- 
ized animals may or may not be protective for 
other animals. Those organisms which cause sys- 
temic infection give rise to leucocytosis (except 
influenza). Local inflammations are accompanied 
by the accumulation of polymorphonuclear leuco- 
cytes. 

I. PNEUMOCOCCUS INFECTIONS PNEUMONIA. 

Xo one organism is the exclusive cause of any organisms 
one type of pneumonia, except perhaps the viruses pneumonia, 
of syphilis and tuberculosis. Any microbe which 
causes pneumonia can also set up inflammations 
in other organs. The following may cause acute 

1. This point is difficult of determination when an organ- 
Ism has little or no pathogenicity for animals (influenza, 
gonococcus, bacillus of Ducrey, etc.). 



502 INFECTION AND IMMUNITY. 

pulmonitis: Diplococcus pneumonia, Streptococ- 
cus pyogenes, Staphylococcus pyogenes, bacillus of 
Friedlander (B. pneumonice) , B. influenza, B. pes- 
tis, B. diphtheria, B. typhosus, B. coli communis, 
B. tuberculosis and Micrococcus catarrlialis. The 
organisms of tuberculosis, actinomycosis, syphilis 
and some other infections cause chronic inflamma- 
tions of the lungs. Some of these organisms have 
already been considered and others will be dis- 
cussed later, in their relation to pneumonia, with- 
out, however, entering into details as to the various 
Dipiococcas types of the disease. The Diplococcus pneumonice 

Pneumonia. • i pi 

is the commonest cause of lobar pneumonia. It 
produces lobular pneumonia not infrequently, and 
has been found as the only organism in acute 
interstitial pneumonia (Weichselbaum). 

Friedlander (1882) found that capsulated cocci 
were present constantly in the exudate of pneumo- 
nia. Such cocci in all probability represented the 
organism which at present is known as the pneu- 
mococcus, yet the cultures which he obtained some- 
what later showed the characteristics of the organ- 
ism now known as the bacillus of Friedlander. 
Fraenkel, in 1884, obtained the first-named coccus 
in pure culture, and his investigations, together 
with those of Weichselbaum and many others, 
eventually established the independence of the 
two organisms. 
Typical and The typical pneumococcus is slightly elongated, 
"strains, and both in the tissues and in culture media it 
grows in pairs. Typically, also, the pair possesses 
a capsule which is present constantly in the tissues 
and may be obtained on certain culture media 
(milk and serum). It is non-motile, non-flagel- 
lated, forms no spores and stains by Gram's method. 






PNEUMOCOCCUS. 503 

Bather scant growth occurs on the ordinary 
culture media in the form of small colonies which 
resemble those of the streptococcus, and unless spe- 
cial media are used it usually can not be carried 
through many generations. When grown in spu- 
tum, or on a medium which contains ascitic fluid, 
the blood or serum of man or some favorable ani- 
mal, its virulence may be preserved for some time. 
By growth at 39° C. virulence is lost rapidly. 
Strains which are atypical in one of several ways 
are encountered. They may show low virulence, 
may grow well at ordinary temperatures (the typi- 
cal organism not doing so), may produce long 
chains in liquid media, or may grow without a 
capsule. 

Eecently the danger of confusing the pneumo- Confusion 
coccus with the streptococcus has received renewed strepto- 
attention, and newer methods of differentiation cocc,ls - 
render it extremely probable that such confusion 
has occurred in the past. An important differen- 
tial method is that of cultivation on agar plates 
which contain blood ( Schottmiiller and Eosenow) ; 
the streptococcus produces a clear zone of hemo- 
lyzed corpuscles about its colonies, whereas the 
colonies of the pneumococcus present a greenish 
color and produce no hemolysis. In using this 
test G. F. Euediger found a surprising number of 
pneumococci in normal throats, whereas previous 
work had shown them to be less common than 
streptococci. 

In spite of the poor viability of the organism on Resistance. 
ordinary culture media, it is fairly resistant to 
desiccation and sunlight, especially when embedded 
in sputum. It is possible that the surrounding spu- 
tum is protective and that the well-formed capsule 



504 INFECTION AND IMMUNITY. 

which the coccus possesses as a parasite, increases its 
resistance. When dried and powdered it is much 
less resistant, being killed by direct sunlight in. 
about an hour. Like other bacteria, it resists 
diffuse sunlight better than direct, and in the 
former may live for as long as 55 days in a dried 
state (Bordoni-Uffreduzzi, cited by Weichsel- 
baum). It has very little resistance to heat, being 
killed by a temperature of 52° C. for ten minutes. 
Toxic No characteristic soluble toxin has been obtained, 
although more or less poisonous substances, some 
of them of a chemical nature, have been described. 
Presumably the toxic properties reside in an endo- 
toxin. The pneumotoxin of F. and G. Klemperer 
was prepared by precipitation with alcohol. The 
pneumococcus is a pyogenic organism and causes 
exudates which are rich in fibrin. Occasionally 
serous rather than purulent exudates are produced. 
Its toxic action is directed toward various organs, 
and it is doubtful if any of the tissues of the body 
are non-susceptible. Some strains are supposed to 
be more neurotoxic than others. 

snscepti- The susceptibility of animals varies greatly. 

Animals. Eabbits and mice are extremely susceptible and are 
used as test animals for the identification of the 
organism. Other laboratory animals have greater 
resistance, and the pigeon and chicken are almost 
absolutely immune. In susceptible animals a rap- 
idly fatal coccemia or more or less extensive local 
lesions are produced, depending on the virulence of 
the culture, the seat of inoculation and the suscep- 
tibility of the animal. In rabbits lobar pneumonia 
has been produced by inoculation into the pleura, 
trachea, blood stream or subcutaneous tissue. 



VIRULENCE. 



505 



Eosenow and others have shown that virulent virulence. 
pneumococci are much less susceptible to phago- 
cytosis than are non-virulent strains. 

By autolysis the substance on which the non- 
susceptibility of virulent pneumococci to phago- 
cytosis depends, can be removed and in this man- 
ner virulent pneumococci rendered readily phago- 
cytable. Furthermore, by treating avirulent 

strains of organisms with the autolytic products 
of virulent organisms, the readily phagocytable - 
non-virulent pneumococci can be rendered less 
susceptible to phagocytosis. This substance, which 
can be extracted from pneumococci and on which 
the resistance to phagocytosis depends, Eosenow 
has called "viralin." Virulin resists boiling for 
two minutes and is insoluble in alcohol and ether. 

The pneumococcus is present in the nose, mouth occurrence 
and pharynx of a large percentage of individuals. in tlie Body * 
It is encountered more frequently in crowded cities 
than in country districts. It persists for weeks 
and months in the mouths of convalescents from 
pneumonia, and it reaches the mouths of those 
who are in the vicinity of pneumonics. It is found 
frequently in the conjunctiva and occasionally in 
the deeper air passages. That it may reach the 
stomach and intestines with the sputum is appar- 
ent, and it has been found there as the cause of 
diphtheric enteritis, a condition which may be 
followed by pneumococcus peritonitis or general 
infection. 

The lungs are infected by inhalation of the Entrance 
cocci. Suspended in droplets of saliva or mucus, 
or adherent to foreign particles, they may be car- 
ried fairly deeply into the bronchial tubes. That 
they ever reach the alveoli by this means alone is 



into Lungs. 



506 INFECTION AND IMMUNITY. 

questioned by many. Two factors would seem to 
prevent their being carried to the alveoli by cur- 
rents of inspired air: First, foreign bodies or in- 
fected droplets are likely to strike and adhere to 
the walls of the respiratory passages before they 
have traversed a great length, and from this situa- 
tion may again be carried out by the action of the 
ciliated epithelium or coughing; the tortuous pas- 
sages of the nose and its hairs and moist surfaces 
arrest many micro-organisms. Second, the velocity 
of the inspired air is greatly reduced or is nil by 
the time the particles might have reached the 
alveoli, a condition which renders their arrest all 
the more probable. Nevertheless, pneumococci do 
reach the alveoli, and by some it is supposed that 
even in health they are carried there more or less 
constantly and are as constantly destroyed. Occa- 
sionally they have been found in the parenchyma- 
tous tissue of the lungs of individuals who have 
died of other than pneumococcus infections or of 
non-infectious diseases. In order to show that 
micro-organisms may be carried into the paren- 
chyma by inspiration Nenninger allowed animals 
to inhale a spray containing Micrococcus prodigio- 
sus, and killing the animals after one-half hour, 
was able to cultivate the coccus from the base of 
the lungs where only alveoli and the finest bron- 
chial branches were present (cited by Weichsel- 
baum). 
Lymphogen- Various other agencies have been suggested by 
Hematogen- which the cocci may be carried to the parenchyma- 
dont tous tissue. For example, during the forced res- 
piratory efforts which accompany coughing they 
may be carried from the bronchial branches into 
the alveoli. Or the organisms having reached the 



INFECTION IN PNEUMONIA. 



bronchi, may be carried through the walls of the 
latter, perhaps by the leucocytes, and reach the 
alveoli directly through the lymph channels or 
after having caused infection in the peribronchial 
lymph glands. Others express the opinion that 
pneumonia follows blood infection in many or 
most instances, i. e., that the infection is hemato- 
genous, the cocci having reached the blood in some 
obscure manner. That the infection may be hem- 
atogenous is shown by the occasional occurrence of 
pneumonia secondary to pneumococcus infection in 
other parts of the body. 

Knowing the fairly constant presence of pneu- 
mococci in the upper respiratory passages in the 
normal individual, it seems certain that some un- 
usual condition must arise to precipitate infection 
of the pulmonary tissue. Concerning the nature 
of these conditions, we have little but theories. 
They may rest either with the microbe or the in- 
dividual, or with both. The pneumococci which 
are normally on the mucous surfaces may undergo 
an increase in virulence, or more virulent organ- 
isms from the outer world, or from pneumonic pa- 
tients, may be inhaled. The latter condition is an 
important one in relation to the contagiousness of 
pneumonia and the development of epidemics. 
Park and Williams found a larger percentage of 
virulent organisms in the sputum of pneumonics 
than in that of normal persons. It is possible that 
the pneumococcus in being passed from one patient 
to another undergoes an increase in virulence, sim- 
ilar to the increase which may be obtained by pass- 
ing bacteria through animals. 

. On the other hand, it is very probable that es- 
sential changes take place in the individual, 



Conditions 
for Infection. 



Decrease of 
Resistance. 



508 INFECTION AND IMMUNITY. 

changes which in some may cause the lowered re- 
sistance which is so often referred to as a condition 
for infection. Exposure to cold has long been 
known as an important predisposing factor, al- 
though we continue in ignorance of its precise 
effects. Animals are more susceptible to pneumo- 
coccus infection after artificial reduction of the 
body temperature. It is possible that a lowered 
body temperature may decrease antibacterial ac- 
tivities; that the activity of the bactericidal fer- 
ments of the plasma or of the leucocytes may be 
suppressed, or phagocytosis may be inhibited so 
that organisms which reach the bronchi and peri- 
bronchial lymphatic structures are allowed to pro- 
liferate. It is probable that in health the leuco- 
cytes continuously pass through the bronchial and 
alveolar walls where they may englobe foreign par- 
ticles (coal dust) or bacteria, and leucocytes are 
present on the mucous membranes of the mouth 
cavity. Following exposure and the reduction of 
the body temperature, or following the prolonged 
inspiration of cold air, the activity of the phago- 
cytes may be inhibited so that cocci which reach 
these surfaces are not ingested and continue to 
proliferate, or the same conditions may decrease 
the exudation of the leucocytes from the vessels. 
It is possible also that the activity of the ciliated 
epithelium is reduced similarly so that the cocci 
are not so readily carried to the exterior. 
other Extreme exposure is not always followed by 
Factors, pneumonia, however, and not all cases of pneumo- 
nia are preceded by exposure; many other condi- 
tions may predispose to infection, as a lowered 
resistance due to alcoholism, other infections or to 
non-infectious processes. That certain local con- 




COMPLICATIONS. 509 

ditions may favor infection is indicated by the fre- 
quency with which individuals with chronic tuber- 
culosis of the lungs die of pneumococcus pneumo- 
nia, and the development of the disease in areas 
of hypostatic congestion. Age is of influence. "To 
the sixth year the predisposition to pneumonia is 
marked; it diminishes to the fifteenth year, but 
then for each subsequent decade it increases" 
(Osier). The cause of these variations is not 
known, although the rise in later years may be 
associated with increased exposure. 

The conditions which predispose to infection are 
now the subject of active study in many labora- 
tories, and the commission which the New York 
Department of Health established for the study of 
acute respiratory diseases made important observa- 
tions as to the prevalence and virulence of pneu mo- 
cocci. 

Many observers have found pneumococci in the compiica- 
blood in a large percentage of the cases, and recent 
work by Eosenow indicates that the blood is prob- 
ably infected in all cases at some stage of the dis- 
ease. This being the case, the frequency with which 
pneumococcus infections occur in other organs as 
complications of pneumonia is readily understood. 
Pleuritis is present almost constantly, pericarditis 
frequently, and the peritoneal cavity is invaded not 
infrequently by way of the diaphragm, with general 
peritonitis as the occasional result. In pneumo- 
coccus pleuritis the exudate is frequently of a 
serous character. Endocarditis, meningitis and 
arthritis are frequent complications. Conjunctivi- 
tis, otitis media, cutaneous or subcutaneous infec- 
tions, intramuscular abscesses and osteomyelitis 






510 INFECTION AND IMMUNITY. 

may develop. The kidneys and liver usually show 
acute degenerations. 

Diplococcus pneumonia occurs as a complication 
in typhoid, diphtheria, tuberculosis, influenza, ery- 
sipelas and other infections, the organism of the 
primary infection also being found in the lungs. 
Not infrequently staphylococci,, streptococci, Mi- 
crococcus catarrhalis, or the bacillus of Friedland- 
er, are found with the pneumococcus, the latter 
being the predominating organism. Eecent work 
from Phipps' Institute (Flick, Eavenell and Er- 
win) suggests that the pneumococcus may be an 
exciting cause of pulmonary hemorrhage in the 
tuberculous. 
Prophylaxis. Prophylactic measures are largely of an individ- 
ual character. One should not come in contact un- 
necessarily with those suffering from pneumonia. 
The susceptible should be guarded against expos- 
ure; pneumonia should be considered as a conta- 
gious disease, the patients should be isolated, the 
sputum disinfected, and rooms cleaned with moist 
antiseptics rather than by dusting and sweeping; 
the sick room should be flooded with sunlight, and 
the mouths of convalescents disinfected. Expecto- 
ration in public places should be limited. To what 
extent the dust-laden atmosphere which prevails 
in most of our large cities is a factor in causing 
pneumonia is unknown. Vaccination is not yet 
an established procedure. 

It is probable that the susceptibility of man 
varies greatly. Under equal conditions of expos- 
ure not all contract pneumonia, and an individual 
who eventually contracts the disease may have 
undergone many similar exposures previously. 
Klemperer introduced a culture of the pneumococ- 



Iiumnnity 
and Suscep- 
tibility. 



RECOVERY. 511 

cus which was virulent for rabbits under his skin 
without suffering more than temporary disturb- 
ance. 

Kecovery seems to indicate an acquired immun- Recovery. 
ity or resistance which is by no means permanent, 
and often is of very short duration. One may have 
as many as eight or ten attacks of pneumonia, the 
intervals between attacks being from three to five 
years on the average (Griswolle). What the re- 
covery or acquired resistance depends on is a mat- 
ter of much discussion. 

Neufeld and Haendel believe that the antibodies 
in pneumonia are inactive until a certain concen- 
tration is reached and that when a high enough 
development of antibodies occurs, there is a sudden 
neutralization of toxins with destruction of pneu- 
mococci leading to the crisis. These authors find 
that the serum of patients, who have passed the 
crisis, is protective for mice against many fatal 
doses of pneumococci. Other observers have failed 
to find any evidence that the crisis is due to anti- 
body production. The marked leucocytosis of 
pneumonia, and the known phagocytic power of 
the leucocytes for the diplococcus, suggest stronglv 
the importance of the leucocytes for recovery. The 
serums of convalescents and of immune animals 
show no increased bactericidal power for the 
organism, nor are they strikingly antitoxic. The 
opsonic power of the serum in pneumonia is 
decreased in the early stages of the disease and 
reaches its height at the crisis and the following 
few days. 

Some of the serums which have been prepared serotherapy 
have been used therapeutically in man, but the re- ation. 
suits have not been sufficiently satisfactory to put 



INFECTION AND IMMUNITY. 



Serum of 
Roemer. 



them on a good basis, although some favorable re- 
ports have been given. 

The serum of Eoemer is obtained by immuniz- 
ing different kinds of animals with several strains 
of pneumococci. The receptor apparatus of differ- 
ent strains probably differ ; hence, a serum obtained 
by immunization with several strains probably 
would be effective against a large variety of pneu- 
mococci. Furthermore, since different animals 
may respond to immunization with a given organ- 
ism by the formation of amboceptors with different 
complementophilous haptophores, a theoretical ad- 
vantage is to be gained by mixing immune serums 
from several animals. The amboceptors of one or 
more of the serums may be susceptible to activa- 
tion by the complement of the patient's body, 
whereas if only one serum were used the chance of 
such activation would be decreased. Passler, in 
summing up the results obtained in the treatment 
of 24 cases with this serum, finds the course of the 
disease shortened, the temperature reduced and a 
tendency to limit the extension of the disease to 
other parts of the lungs. According to Neufeld 
and Haendel the disadvantage of the various anti- 
serums lies in ihe fact that they cannot readily be 
given in large enough doses to be effective. 

The serum of pneumonia patients shows an in- 
creased agglutinating power for the pneumococcus. 
The maximum is reached at or near the time of 
crisis, but rarely has a higher value than 1 to 50 
to 1 to 60 (JSTeufeld, Eosenow). It disappears 
quickly after recovery. In immunized animals the 
agglutinating power may be pushed to much higher 
limits. Not all strains yield agglutinins equally, 
and not all are agglutinated equally by the same 






TREATMENT. 



513 



serum. According to Collins, pneumococci fall 
into different groups, depending on their agglu- 
tinable properties; the same author determined 
the presence of group agglutinins in an immune 
serum. Neufeld states that avirulent strains were 
not agglutinated by the serum of pneumonic pa- 
tients. 

Beginning with Fraenkel (1886), many have 
shown the possibility of increasing the resistance 
of susceptible animals to the pneumococcus by in- 
jecting first dead or avirulent and then virulent 
cultures; in this way the subjects can be made to 
withstand many multiples of the minimum fatal 
doses. Eosenow has been able to separate, by a 
process of autolysis, the more toxic part of the 
pneumococcus, and the bodies of the organisms. 
By the use of the non-toxic part as antigen, a 
more rapid development of antibodies can be- 
obtained, experimentally, than can be accom- 
plished with whole pneumococci; Eosenow has 
made this fact the basis of treatment of pneu- 
monia by means of injection of the autolyzed bod- 
ies of pneumococci and has obtained encouraging 
results. It is hoped that this procedure will be a 
valuable aid in hastening the crisis. 



Vac c in 
Treat n 



OTHER INFECTIONS BY THE PNEUMOCOCCUS. 

Complicating infections by the pneumococcus 
during the course of pneumonia were mentioned 
above. They may occur by way of the lymph 
channels, as in pleuritis, pericarditis and peritoni- 
tis (through the diaphragm), by continuous exten- 
sion, as in infection of the bronchi, nose and, per- 
haps, the middle ear, or as metastatic infections 
following the invasion of the blood stream by the 









Infection. 



514 INFECTION AND IMMUNITY. 

organisms. It is undoubtedly in the last named 
manner that meningitis, endocarditis, arthritis, 
and muscular and subcutaneous abscesses arise. 

Rosenow has isolated from endocarditis cases 
pneumococci differing from the usual type in that 
they grow in clumps and adhere more or less 
closely to the surface of blood-agar slants. They 
grow in chains and produce less green on blood- 
agar plates than do pneumococci of the usual type. 
In animal inoculation a tendency to localize on 
endothelial surfaces is shown. 
Mode of Other infections by the pneumococcus occur in- 
dependent of the existence of pneumonia. Such 
conditions are alveolar abscesses, conjunctivitis, 
dacryocystitis, serpent ulcer of the cornea, in- 
flammation of the middle ear, meningitis, enteri- 
tis, rarely peritonitis, and pneumococcus septice- 
mia which may be complicated by infection in vari- 
ous organs. The eye is exposed to infection from 
without and the ear from the pharynx. Primary 
pneumococcus meningitis occurs both sporadically 
and epidemically, although the meningococcus is 
a much more frequent cause. The organisms may 
gain entrance through the middle ear or nose, or 
through the circulation from a primary focus in 
another organ, perhaps an undiscovered focus. Pre- 
ceding and during meningitis the nose is not in- 
frequently the seat of pneumococcus rhinitis, and 
the organisms may be carried from the nose to the 
meninges by way of the lymph channels. The 
blood may be infected secondarily. Pneumococcus 
meningitis is almost invariably fatal. The organ- 
ism causes chronic meningitis less frequently than 
the meningococcus. Infection of the peritoneum 



STREPTOCOCCUS. 515 

may follow an intestinal infection ; a pure pneumo- 
coccus infection of the peritoneum in the absence 
of pneumonia is extremely rare. Pneumococcus 
infections of the eye, ear, intestines and perito- 
neum are likely to be accompanied by other or- 
ganisms. 

Pneumococcus conjunctivitis occurs in epidemic 
form and the same precautions should be taken 
to limit it as for the limitation of influenza con- 
junctivitis. 

Serpiginous ulcer of the eye,. a progressive phag- 
edenic process in the cornea, is usually caused by 
the pneumococcus, although other organisms may 
be present. Eoemer treats the condition with 
an antipneumococcus serum and claims that he is 
able to arrest the process if the treatment is begun 
sufficiently early. The serum is injected beneath 
the conjunctiva. 

II. STREPTOCOCCI. 

When wound infections, cases of septicemia and Discovery of 

" Pyogenic 

pyemia were first studied bacteriologically, various cocci. 
names were applied to certain cocci which were 
found. Such were the Microsporon septicum of 
Klebs and the Coccobacteria septica of Billroth 
and others. Pasteur recognized such organisms 
and cultivated them at an early date, but Ogsten, 
in 1880 to 1884, using the newly-devised technic 
of Koch, was the first to recognize two sorts of 
pyogenic cocci, to which he gave the names of strep- 
tococci and staphylococci. The former grew in the 
form of chains and the latter in clusters. In 1883 
Fehleisen obtained the streptococcus in pure cul- 
tures from cases of erysipelas. Eosenbach deter- 
mined more exactly the significance of streptococci 



516 INFECTION AND IMMUNITY. 

in wound infections and septicemia, and gave to 
the organism the name of Streptococcus pyogenes. 
Morphology. The typical streptococcus is a spherical or 
spheroidal cell, about one micron in diameter, 
which grows in the form of chains of varying 
length. Division takes place in one direction 
only. Variations in form, such as diplococcus-like 
cells in pairs or chains, or elongated cells resem- 
bling bacilli, represent accidental stages or anoma- 
lies in division. Streptococci commonly appear as 
diplococci in the blood and tissues of the infected. 
Unusually large cells may be involution forms. 
The difficulty of distinguishing the pneumococcus 
from the streptococcus has been mentioned. At 
one time it was thought that streptococci could 
be separated into those which grew in long chains 
(8. longus) and those which produce short chains 
(8. brevis) . Although these names are still used 
for convenience, they are not well grounded, since 
the length of the chains is not an inherent prop- 
erty; one form may be changed into the other by 
appropriate methods of cultivation. Similarly the 
8. erysipelatis of Fehleisen is not a specific or- 
ganism for erysipelas, since strains from other 
sources are able to cause experimental erysipelas 
in man. Streptococci growing in short chains may 
be cultivated from the normal mouth cavity and 
they are usually of low virulence for animals. On 
the other hand, 8. longus is more often obtained 
from wound infections, septicemia and malignant 
tonsillitis. Capsulated strains of high virulence 
are occasionally found in the body. Ordinarily, 
however, streptococci are not surrounded by a cap- 
sule. The Streptococcus mucosus may be a pneu- 
mococcus. Although streptococci are described 



STREPTOCOCCUS. 



which do not stain by Gram's method, those with 
which we are concerned invariably react positively. 
Streptococci are never motile, possess no flagellar 
and form no spores. 

Streptococci grow better in a neutral or slightly 
alkaline medium than in one of acid reaction, but 
virulence is lost rapidly. They may be cultivated 
indefinitely in media which contain serum or 
ascitic fluid, but even here virulence disappears 
gradually; frequent transplantation is necessary. 
In bouillon those strains which produce short 
chains or grow as diplococci cause a diffuse cloud- 
ing of the medium, whereas those growing in long 
chains sink to the bottom, leaving a clear overly- 
ing fluid. Streptococci demand little oxygen, all 
are facultative anaerobes and some are said to be 
obligate anaerobes; obligate anaerobes may be cul- 
tivated from the vagina and intestines. The 
optimum temperature for growth is 37° C. 

When dried, streptococci live for from ten days 
to several weeks; they are destroyed more quickly 
in the presence of sunlight. Susceptibility to 
antiseptics depends on the nature of the medium 
in which they are suspended or imbedded. When 
unprotected by bouillon or other fluid they are 
killed in a few seconds by 1/1000 corrosive sub- 
limate and 3 per cent, carbolic acid (Fehleisen) ; 
when in bouillon, by 1/1500 corrosive sublimate 
and by 1/200 carbolic acid in fifteen minutes. Ly- 
ing on a mucous surface, where they are imbedded 
in mucus or tissue fluids, they are protected 
against antiseptics to some extent. They are fairly 
resistant to heat, being destroyed by a temperature 
of 70° to 75° C. in one hour (v. Lingelsheim). 



Cultivation. 



Resistance- 



518 



INFECTION AND IMMUNITY. 



vimience. Streptococci vary widely in their pathogenicity. 
Cultures which are entirely non-pathogenic for 
animals are frequently cultivated from nature and 
from man. As a rule, however, the long chains 
obtained from pathological processes in man are 
pathogenic for rabbits and mice. Their virulence 
is very labile, and by passage through suitable ani- 
mals (rabbit, mouse) it may be pushed to a very 
high point; in doing this, however, the original 
virulence of the culture undergoes modifications. 
For example, Marmorek so increased the virulence 
of one strain that the millionth part of a cubic 
centimeter was fatal for rabbits, but it had lost its 
pathogenicity for man, as shown by inoculations 
into carcinomatous patients. Hence the patho- 
genicity of cultures for animals is not a good 
index of their virulence for man. Those which 
produce long chains in bouillon are more patho- 
genic than those forming short chains (v. Lingel- 
sheim). 

Rabbits and mice are the most susceptible ani- 
mals. The rat, guinea-pig and cat, and larger ani- 
mals, as the horse, goat and sheep, are less sus- 
ceptible. A bouillon culture of which from 0.01 
to 1.0 c.c. will kill a mouse or rabbit in from one 
to four days is considered of high to moderate 
virulence. Virulent cultures cause systemic infec- 
tion, regardless of the method of inoculation. 
Less virulent cultures produce changes which are 
more localized in character and which may heal : 
abscesses, areas of necrosis and erysipelatous 
inflammations. 

The properties on which the virulence of strepto- 
cocci depends are little understood. The conflict 
of opinion concerning many points probably de- 



Endotoxin. 



STREPTOCOLYSIN. 519 

pends on the use of different strains of the organ- 
ism in experimental work. The amount of endo- 
toxin which virulent strains contain is subject to 
great variations. Aronson found practically none 
in the killed cells of a very virulent strain. It 
seems probable that the endotoxin is rather sus- 
ceptible to heat, since cultures which are killed 
by mild methods, as by chloroform, are more toxic 
than those which are killed by heat. The filtrates 
of old bouillon cultures are more or less toxic. A 
strong "toxin" was prepared by Marmorek by 
growing a virulent strain in a mixture of serum 
and bouillon for three months and filtering the 
culture. More recently he uses a medium contain- 
ing glycocol and leucin. Toxic precipitates from 
fluid cultures have also been obtained. Bouillon 
filtrates of virulent cultures after two to fourteen 
days of growth have low toxicity (Aronson). 

Besredka, and later G-. F. Euediger, showed that streptoco- 
virulent streptococci produce a hemolytic toxin Leacocytic 
when grown in various heated serums. Euediger 
proved that this hemolysin (streptocolysin) is a 
true toxin, possessing a haptophorous and toxo- 
phorous structure. This discovery has an im- 
portant bearing on the fact that the blood in fatal 
streptococcus infections, especially in rabbits, is 
often more or less laked. Streptocolysin is de- 
stroyed by a temperature of 70° C. in two hours, 
by peptic digestion, deteriorates rapidly at ordi- 
nary temperatures, and is non-dialysable. Certain 
normal serums contain antistreptocolysin (Eue- 
diger). Another significant fact is that virulent 
strains, when grown in serum and ascitic fluid, 
produce a substance which kills leucocytes and 
inhibits phagocytosis. This may explain the fail- 



Processes. 



520 INFECTION AND IMMUNITY. 

ure of leucocytes to take up virulent organisms, 
whereas non-virulent strains are readily phagocy- 
tized. Von Lingelsheim states that strains culti- 
vated from subacute or chronic processes produce 
more soluble toxin (nature unknown) than highly 
virulent strains. Not all toxic filtrates contain 
streptocolysm, the hemolysin being independent 
of other toxic constituents (Simon). Yon Lingels- 
heim concludes that the infectiousness of strepto- 
cocci is not explained by the toxic properties which 
have been demonstrated. He lays stress on their 
resistance to the bactericidal activities of the tis- 
sues and tissue fluids. It is safe to say that up to 
the present time the essential toxin of the strepto- 
coccus has not been demonstrated. 
Pathologic Streptococci are the frequent cause of wound in- 
fections, the most common cause of lymphangitis 
and diffuse inflammations of the subcutaneous and 
intermuscular connective tissues (cellulitis), endo- 
metritis and puerperal septicemia, endocarditis 
and tonsillitis, are often the exciting organisms 
in pneumonia (lobular, usually), bronchitis, 
meningitis, inflammations of the serous surfaces 
(pericardium, pleura, peritoneum joints), enteritis 
and suppurative processes in the middle ear. They 
are the exclusive cause of erysipelas, and serious 
attempts have been made to show that they are 
etiologic factors in scarlet fever and rheumatic 
fever. The streptococcus is the most common 
organism found in the lesions of impetigo conta- 
giosa, although it may be mixed with other bac- 
teria, especially the staphylococcus. Occurring as 
mixed infections in pneumonia, tuberculosis, scar- 
let fever, enteritis and other processes, they cause 
grave and often fatal complications. 




ERYSIPELAS. 



521 



Not all streptococci are able to cause erysipelas, 
and a streptococcus cultivated from a case of ery- 
sipelas is not able to cause the disease in all indi- Erysipelas. 
vi duals. Furthermore, cultures obtained from 
other sources (phlegmon) may produce the dis- 
ease (Koch and Petruschky). Koch produced an 
erysipelatous inflammation with staphylococcus. 
It has been suggested that streptococci which 
cause erysipelas, rather than some other process, 
do so because of some peculiarity in their virulence 
or in the resistance of the individual, or perhaps 
both. Another suggestion is that this type of in- 
fection depends on some peculiarity in the skin 
and subcutaneous tissue of the susceptible. The 
conditions are obscure. The infection atrium is 
not always known. In facial erysipelas entrance 
probably is gained through the mucous membrane 
of the nose in many instances. Erysipelas is a 
wound infection in most or all instances, although 
the atrium often escapes observation. The cocci 
lie principally in the lymph spaces and interspaces 
of the connective tissue. They are rarely to be 
cultivated from the scales or the fluid of blisters, 
but may be obtained from skin which is excised 
from the border of the inflamed area (Fehleisen). 
They probably are not excreted through the un- 
broken skin. 

Erysipelas is an inflammation of the superficial Lympiian- 
lymphatics of the skin, while in lymphangitis the »' ltis - 
deeper lymphatics are involved. Thrombosis of 
the lymphatic vessels, congestion of the adjacent 
blood vessels, causing reddened streaks and local 
hemolysis (?), are distinguishing local features. 
Metastases occur to adjacent lymph glands and 
the infection may become general. In this process, 






522 INFECTION AND IMMUNITY. 

as well as in wound infections, thrombosis of the 
adjacent vessels may occur, which may be the first 
step in the production of pj^emia with multiple 
points of infection. 

Cellulitis may also be caused by the staphylo- 
coccus alone or infection with the latter may be 
superimposed on a primary streptococcus cellulitis. 
Pneumonia. Pneumonia produced by the streptococcus may 
either be primary or secondary to infection in 
other parts of the body. It is mostly of the lobular 
type in the occurrence of multiple foci, which pre- 
sent a smooth surface on section and are very rich 
in cells. It occurs less frequently in the form of 
lobar consolidation, and very frequently as a mixed 
infection in pneumonias caused by the pneumo- 
coccus and other organisms. 

Streptococcus infection of the lungs in pul- 
monary tuberculosis is a serious and frequent com- 
plication of the latter disease. It produces a septic 
condition, involves adjacent healthy tissue, and its 
role in causing consolidation and liquefaction of 
the tissues predisposes of hemorrhages. In cul- 
tures, the streptococcus is said to inhibit the 
growth of the tubercle bacillus. 
Meningritis. Primary streptococcus meningitis is rare or of 
doubtful occurrence. It frequently is secondary 
to otitis media, to injuries, and has been noted 
following tonsillitis, facial erysipelas, pneumonia, 
endocarditis and as part of a pyemic process. 
Enteritis. Streptococci are at times the cause of enteritis 
in children, the inflammation often being mem- 
branous and accompanied by desquamation of the 
epithelium and by hemorrhages. It is not infre- 



STREPTOCOCCUS INFECTIONS. 523 

quently followed by peritonitis and septicemia. 
Virulent organisms probably reach the intestines 
through milk in many instances. Escherich found 
streptococci in nearly every sample of milk which 
he examined. Digestive disturbances due to other 
causes predispose to infection. The organisms are 
nearly always present in the intestines of the 
adult, but cause enteritis less frequently than in 
children. 

The normal vagina does not offer a good cul- 
ture medium for pathogenic bacteria, although 
streptococci are occasionally found there. They 
occur more frequently in those who have borne 
children. The vagina tends to purify itself me- 
chanically and by the acid nature of its secretions. 
If the secretion for any reason becomes alkaline, 
as in catarrhal conditions, or if it contains blood 
and serum, which provide a good culture medium, 
virulent streptococci proliferate. Infection takes 
place through denuded surfaces and tears; endome- 
tritis, metritis, parametritis, salpingitis, peri- 
tonitis and sepsis may follow. Thrombosis of the 
blood vessels may be followed by the development 
of pneumonic foci. 

Streptococci are probably always present on the 
tonsils, the mucous membrane of the mouth, very 
frequently in. the sputum and not infrequently on 
the mucous membrane of the anterior nares. Pre- 
sumably they proliferate under inflammatory con- 
ditions from whatever cause, finding in the serum 
and plasma which exude a medium favorable for 
growth and the development of virulence. They 
are of great significance in severe local inflamma- 
tions, as in diphtheria and scarlatina, and when 



Vagina 
and Uterns. 



Respiratory 



524 INFECTION AND IMMUNITY. 

general resistance is lowered, as in typhoid, typhus, 
variola, measles, etc. Von Lingelsheim character- 
izes their relation to diphtheria as follows : they 
injure the tissues locally, penetrate beneath the 
membrane into the tissues and take part in the 
formation of the membrane; they increase the 
virulence of the diphtheria bacillus; alone, or in 
conjunction with the diphtheria bacillus, they may 
invade the lungs, causing bronchopneumonia, or 
enter the circulation and injure various organs, 
but particularly the kidneys. Their method of 
entering the lungs from the upper respiratory pas- 
sages probably is similar to that involved in pneu- 
mococcus infection. Furthermore, having obtained 
a footing in the pharynx, for example, they may 
reach the bronchi and perhaps the alveoli by exten- 
sion along the surface. 

Streptococci are usually the essential organisms 
in follicular tonsillitis, are frequently found in 
alveolar abscesses, but in both instances may be 
mixed with other organisms, especially the staphy- 
lococcus and pneumococcus. Streptococci in the 
throat may appear in diplococcus form in fresh 
preparations. Beginning primarily in the nose, 
tonsils or pharynx, streptococcus infection may 
extend to the adjacent sinuses, the middle ear, 
meninges, or through the tonsils may cause sys- 
temic infection with endocarditis as a frequent 
complication. 
Endocarditis. The endocarditis caused by streptococci usually 
is vegetative in character, but may be ulcerative, 
and may result in metastatic foci of infection 
(e. g., septic infarcts). Infarcts from strepto- 
coccus endocarditis are not always infected, how- 




Fever. 



RHEUMATIC FEVER. 525 

ever. Not infrequently the vegetations contain 
staphylococci as well as streptococci. 

Since 1867, when Salisbury described a fungus Rheumatic 
which he called Zy mo to sis translucens,many micro- 
organisms have been described and cultivated from 
the joints, blood, endocarditic and pericarditic 
lesions and from the tonsils in acute articular 
rheumatism. Among them were the "Monadinen" 
of Klebs (1875), short bacilli by Wilson (1885) 
and others, staphylococci and streptococci by 
Weichselbaum (1885) and by many others, and 
an anaerobic bacillus resembling that of anthrax 
by x\chalme (1890). Streptococci have been found 
more frequently than other organisms. The ba- 
cillus of Achalme acquired considerable prominence 
at one time, being found in rheumatism in a num- 
ber of cases, but it has been found since in other 
conditions, and normally, and Achalme himself 
gave up his original claims for its etiologic 
significance. The organism, possibly, is identical 
with B. aerogenes capsulatus of Welch (Harris). 
Many of the observations are of little value, since 
the cultures were made postmortem, when contami- 
nations and agonal invasions by other organisms 
could not be excluded. The conditions were very 
confusing, however, since the injection of pure 
cultures occasionally produced arthritis, peri- 
carditis and endocarditis in animals. This was 
the case with a short anaerobic bacillus or diplo- 
bacillus cultivated by Thiroloix, and by Triboulet, 
Coyon and Zadoc (1897). 

In 1897-98 Triboulet and Coyon cultivated from 
the blood of five cases of rheumatic fever a diplo- 
coccus, pure cultures of which caused arthritis, 



526 INFECTION AND IMMUNITY. 

endocarditis, etc., in rabbits. Similar observations 
have been made by Westphal, Wassermann and 
Malkoff, Poynton and Paine. Beaton and Walker 
and others, and the possibility of producing lesions 
characteristic of rheumatic fever by the inocula- 
tion of pure cultures into rabbits has been well es- 
tablished. Although the organism was called a 
diplococcus by the discoverers, it can not be dis- 
tinguished from the ordinary streptococcus pyo- 
genes by cultural tests. These discoveries do not, 
however, put this particular streptococcus on a 
satisfactory basis as the cause of the disease, since 
streptococci from various sources are able to cause 
experimental arthritis in rabbits (Cole, Harris). 
It seems that virulent streptococci from whatever 
source have a predilection for serous surfaces. This 
is apparent from the frequency with which the 
joints, endocardium, etc., are involved in strepto- 
coccus septicemia in man. The view of Singer 
and of Menzer that "acute rheumatism is simply 
one of the many manifestations of streptococcus 
invasion" (Harris), finds some justification in 
the streptococcus tonsillitis with which the dis- 
ease usually begins, the recovery of streptococci 
from the lesions and the production of these lesions 
in rabbits by the injection of pure cultures. Tun- 
nicliff found that the opsonic indices for M. rlieu- 
rrjfiicus (Beattie, Poynton and Paine) for Strep- 
tococcus viridans from the throat of a patient with 
rheumatism and for Streptococcus pyogenes fol- 
low the same course during attacks of rheu- 
matism. In cases with joint symptoms and 
high temperature the index was subnormal and 
with improvement in clinical symptoms it 






SCARLET FEVER. 527 

rose above normal. The indices for Staphy- 
lococcus aureus, pneumococcus and a strain of 
Streptococcus viridans from a normal throat 
did not show a variation from the normal. 
Agglutinins common to M. rheum aticus and strep- 
tococci were found to follow the same course as 
the opsonic index. Immunization of rabbits with 
M. rheumaticus resulted in the formation of opso- 
nins for both this organism and Streptococcus 
pyogenes. These findings would indicate that 
streptococci play an essential part in acute articu- 
lar rheumatism. The fact remains, however, that 
streptococci cannot always be cultivated from the 
lesions of rheumatic fever; hence it is possible that 
the organism may exist as a mixed infection with 
more or less constancy, and that the real cause is 
as yet unknown (Phillip). 

The theory that scarlet fever is of streptococcus Relation of 
etiology has been held particularly by Babes, to^carfet 001 
Klein, Moser, Gordon and Baginsky and Sommer- Fevep * 
feld. Some have held that streptococci isolated 
from the disease show distinctive properties and 
deserve the name of Streptococcus scarlatina. This, 
however, is not agreed to by most bacteriologists, 
the organisms not differing from streptococci ob- 
tained from various sources. The organisms are 
not found constantly in the erythematous eruption. 

Virulent streptococci are found on the tonsils 
almost invariably in scarlet fever. In 65 per cent, 
of the cases a membrane is formed (Kanke), and 
this is often due to the streptococcus, which is 
sometimes, however, associated with diphtheric 
infection. The frequency with which streptococci 
invade the blood during scarlet fever is related to 
the severity of the disease. Occasionally they are 



528 INFECTION AND IMMUNITY. 

found in mild cases, which run a short, uncompli- 
cated course, but "more frequently in severe and 
protracted cases, in which there also may develop 
local complications and clinical signs of general 
infection, such as joint inflammations" (Hek- 
toen). Baginsky and Sommerfeld found strepto- 
cocci in the blood and organs of each of eighty- 
two fatal cases. Hektoen states, however, that 
streptococcemia is not necessarily present in fatal 
cases. 

Gabritschewski and other Eussians have reported 
satisfactory results following prophylactic vacci- 
nation against scarlet fever by means of killed 
streptococci from scarlet fever patients. They 
advance this experiment as an argument in favor 
of the streptococcus as the sole cause of scarlet 
fever. The results, however, have Dot yet been 
confirmed by other observers. 

At present there is not sufficient ground for con- 
sidering streptococci as the specific agent in scarlet 
fever, although they are undoubtedly the cause of 
the most frequent and serious complications. The 
mortality of the disease probably is greatly raised 
by mixed infections with the streptococcus. 

Streptococcus filtrates or cultures may cause de- 
generative changes in the spinal cord (Homen 
andLaitinen). 
Beneficial Certain strains of streptococci are said to exer- 
cise a curative effect in experimental anthrax. 
Von Emmerich and di Mattei found that by intra- 
venous injection of the cocci rabbits could be saved 
from an anthrax infection which otherwise would 
prove fatal in forty-eight hours. This result can 
not always be obtained, and it may be that only 






Influences. 



IMMUNITY TO STREPTOCOCCUS. 529 

certain strains have this effect (Zagari, cited by 
v. Lingelsheim). It is noted occasionally that lupus 
improves or actually heals following an attack 
of erysipelas. A reputed effect of a similar nature 
in tuberculosis of the lungs was mentioned above. 

The clinical observation that an attack of 
erysipelas often causes a decrease in the size of fjfreo*^ 
malignant tumors, especially sarcomas, received 
some confirmation from the experimental work of 
Fehleisen. With the hope of reproducing erysipe- 
las with pure cultures, Fehleisen had inoculated 
streptococci into those suffering from such tumors. 
Among six patients so inoculated, a decrease in the 
size of the tumor was noted in five. Killed cul- 
tures were tried without effect. Coley's mixture 
of killed cultures of the streptococcus and Bacillus 
prodigiosus received rather extensive trial as a 
substitute for living cultures of the streptococcus, 
and in many instances improvement and even 
cures have been reported. Others have had no 
favorable results. Senn used the preparation in 
twelve cases of inoperable sarcoma "with negative 
results/' The Bacillus prodigiosus is supposed in 
some way to increase the efficacy of the strepto- 
coccus toxin; it contains a toxic protein. These 
toxins seem to have no influence on carcinomas. 

Concerning the natural susceptibility and im- 
munity of man to infections with the streptococcus ImMi w^ity 

J *■ ana suscep- 

little is known. It seems probable that the un- tiMiity. 
impaired mucous surface resists invasion by the 
organisms which occur constantly in the mouth 
cavity; the physical protection of the intact sur- 
face, the rapid desquamation of epithelium, the 
rapid excretion with the saliva, the inhibiting in- 
fluence of the saliva on the proliferation of bac- 



530 INFECTION AND IMMUNITY. 

teria and the destruction of bacteria by the leuco- 
cytes which constantly appear on the mucous sur- 
face are probably important factors in this local 
resistance. Congestion of these surfaces, espe- 
cially the tonsils, from any cause, as from ex- 
posure, or the occurrence of some other infection, 
as may be the case in scarlet fever, may lower the 
local protective powers. And, as stated, the serum 
and plasma which exude in catarrhal conditions 
or other inflammations, provide a medium which 
favors the growth and development of virulence 
by streptococci. 

Concerning the conditions which, in the body, 
antagonize infection, we are largely in the dark. 
It has been impossible to demonstrate antitoxic 
and bactericidal substances in the normal serum 
of man. Streptococci grow freely in fresh normal 
serum which contains no leucocytes (Weaver and 
G. F. Euediger). Phagocytosis of streptococci 
first came under the observation of Metchnikoff, 
who in 1887 noted it as a striking occurrence in 
erysipelas. Only the macrophages took up the cocci. 
The marked leucocytosis which is noted clinically 
suggests, but of course does not prove, that the 
leucocytes take an active part in the destruction 
of the cocci. Experimental work showing such a 
relationship is not lacking, however. Bordet con- 
cluded that all the protection which guinea-pigs 
and rabbits show against streptococci is due to 
the phagocytes. In actual infection streptococci 
have often been found within the leucoc} T tes of 
the blood and inflammatory exudates (G. F. Eue- 
diger.) Non- virulent or weakly virulent strains 
are phagocytized more readily than the virulent in 
experimental work. Ruediger also demonstrated 



IMMUNIZATION OF ANIMALS. 531 

conclusively that the streptococci taken up by poly- 
morphonuclear leucocytes may be killed by the lat- 
ter. Hence the evidence in favor of a protective 
role by the leucocytes is more than presumptive. 
Ruediger suggests the importance of the leuco- 
cytic toxin of the streptococcus for the develop- 
ment of infection. It may either kill the leuco- 
cytes or cause negative chemotaxis, and under these 
conditions proliferation of the cocci may proceed. 

Weaver, Tunnicliff and Boughton have shown 
that the defense of the body against streptococci 
depends on the power of phagocytosis on the part 
of the leucocytes as well as the opsonin, hence the 
estimation of the resisting power of the body must 
be measured by the bactericidal power of whole 
blood. 

The streptococcus usually is classed with those Acquired 
organisms, infection with which does not cause the 
development of lasting immunity. A certain 
amount of immunity probably is established, how- 
ever. This is suggested by the results of Fehlei- 
sen, who could not always cause second attacks 
of erysipelas by the inoculation of pure cultures 
into the susceptible. It is also suggested by the 
ease with which relatively high resistance can be 
produced in animals by brief immunization. A 
streptococcus infection of the horse which occurs 
naturally ("Druse") is said to produce immunity 
which lasts for a year or two. 

One may immunize animals either with toxic i,,,,,. mi in- 
filtrates or with killed and living cultures. The Animals. 
filtrates are much less effective in producing im- 
munity than the bacterial cells, and in the hands 
of many no immunity whatever could be estab- 
lished. 



INFECTION AND IMMUNITY. 



Unity or Mul- 
tiplicity of 
Streptococci. 



A number of different principles have been fol- 
lowed in immunizing with cultures. It seems that 
virulent strains cause a higher degree of immunity 
and a serum of higher protective power for other 
animals than strains of low virulence. On this 
account Marmorek, and also Aronson, immunize 
horses with streptococci, the virulence of which has 
been pushed to a very high point by passing them 
through rabbits. Strong resistance is induced by 
this method, and the immune serum, particularly 
that of Aronson, shows distinct protective power 
for other animals. Such serums, however, have 
the highest protective power against the particu- 
lar strain which was used for immunization, al- 
though the serum of Aronson is not devoid of pro- 
tective powers against other pathogenic strains. 
Concerning the serum of Marmorek there are di- 
vergent opinions. In the hands of Marmorek it 
is highly protective in animal experiments; others 
have found it without value. The method of Mar- 
morek and of Aronson rests not only on the basis 
that strains of the highest virulence will give the 
strongest serums, but also on the assumption of 
the unity of all pathogenic streptococci. If all 
are alike in their biologic and pathogenic proper- 
ties, a serum which protects against one should 
protect against all. As pointed out, there is at 
present not sufficient ground for considering the 
streptococci of erysipelas, scarlet fever, rheuma- 
tism, sepsis, etc., as independent species. By cul- 
tivation and passage it is possible to so modify any 
one of them that it is indistinguishable from the 
others, on the basis of morphology and patho- 
genicity. On the other hand they are not all 
identical in some very important properties. For 



STREPTOCOCCIC SERUMS. 533 

example, not all strains produce hemolysin to the 
same degree, and they differ greatly in their sus- 
ceptibility to the action of an agglutinating serum. 
We have also to remember that pathogenicity for 
animals is not a reliable index of pathogenicity for 
man. From these confusing conditions we can 
only regard the question of unity or multiplicity 
of streptococci as an open one, which may be de- 
cided by future investigations. 

The serums of Marmorek and Aronson are uni- univalent and 

• • -, PolTA-aleat 

valent serums, a single strain being used for 1m- semms. 
munization. Certain investigators, believing in 
the multiplicity of streptococci, utilize several 
strains in immunization. The serum of Denys is 
obtained by immunizing with several strains the 
virulence of which has been artificially increased. 
Such a serum would, theoretically, have a wider 
range of action than a univalent serum ; it is poly- 
valent. Having in mind the fact that passing a cul- 
ture through rabbits increases the virulence of 
the organism for the rabbit, but alters its virulence 
for the original host (man), Tavel, Moser and 
Menzer prepare serums on a different basis. 
Tavel employs several strains of streptococci cul- 
tivated from pathological processes in man, avoid- 
ing such alterations in virulence as would be caused 
by passing the cultures through animals. On the 
assumption that scarlet fever is a streptococcus 
disease, Moser immunizes horses with strains 
(about twenty) which are cultivated from cases 
of scarlet fever. In a similar manner, Menzer, 
"supposing that rheumatic fever is a streptococcus 
infection, immunizes with a number of strains cul- 
tivated from the tonsils of cases of rheumatism. 
Both Moser and Menzer avoid passage in order to 



INFECTION AND IMMUNITY. 



Serum 
Protection. 



Serum 
Therapy. 



retain the original biologic properties of the cul- 
tures. 

In animal experiments, some of these serums, 
and particularly that of Aronson, have exhibited 
strong protective powers. Aronson's serum in 
doses of 0.0004 to 0.0005 c.c. protects a mouse 
against ten fatal doses of the streptococcus given 
twenty-four hours later than the serum. A serum 
of which 0.01 c.c. protects against a dose known 
to be fatal is considered of normal strength. The 
present serum, then, is of twenty- to twenty-five- 
fold value. In some instances animals can be 
saved when the serum is used some hours after 
infection, but this period is a brief one. 

Statements concerning the value of antistrepto- 
coccus serums in treating human infections are 
very conflicting. The serum of Marmorek has 
been given more general trial than any other, and 
the results have not been satisfactory. Favorable 
effects, such as the lowering of temperature and 
improvement in the general condition, have been 
reported, but the serum possesses no distinct cura- 
tive power in established infections. Koch and 
Petruschky deny that it has a proph}dactic power 
in experimental erysipelas. Escherich, by using 
the serum of Moser, and Baginsky, by using that 
scarlet of Aronson, observed a shortening of the course, 
Fever. a rec [ ue ^ ori f ^he f ever arL( j general improvement 
in cases of scarlet fever. Moser claims that it re- 
duces the mortality of the disease. The use of 
anti streptococcus serum in the treatment of scarlet 
fever does not commit one to the streptococcus 
etiology of the disease, but rather to the impor- 
tance of streptococcus complications ; hence, if the 
danger of these complications can be reduced by 



.STREPTOCOCCIC SERUMS. 



Properties 
of Serum. 



antistreptococcus serum its use is justified. It 
remains for future work to demonstrate to our 
satisfaction that it has such value. 

What has been said concerning the treatment of Rheumatism. 
scarlet fever with the serums of Moser and Aron- 
son also applies to the treatment of rheumatism 
with the serum of Menzer. Favorable reports have 
appeared concerning its value, but a sufficient mass 
of experience has not accumulated to permit of 
satisfactory judgment. "So much appears from 
observations in man that the different streptococcus 
serums are harmless" (Dieudonne). 

As nearly as can be learned at present, anti- 
streptococcus serum is protective (and cura- 
tive ( ?) ) because of its ability to stimulate phago- 
cytosis, rather than because of serum antitoxins 
or bacteriolysins. This was indicated by the ob- 
servations of Bordet in animal experiments, in 
which marked phagocytosis of streptococci took 
place in the peritoneal cavity of immunized ani- 
mals, but very little in normal animals. A simi- 
lar condition was noted in the test-glass experi- 
ments of Denys and van der Velde. A mixture 
of normal rabbit serum and leucocytes showed 
very little phagocytosis of streptococci, whereas 
the addition of antistreptococcus serum caused 
active phagocytosis, with death of the cocci. The 
presence of a definite substance in the serum which 
stimulated phagocytosis was conceived by van cler 
Velde and also by v. Lingelsheim. It was heat- 
resistant (62° to 65° C), and was not destroyed 
by dilute acids and alkalies (cited by Lingelsheim). 

The proph}dactic injection of killed streptococci 
in scarlet fever has been mentioned. 



Stimulation 
of Phagocy- 
tosis. 



Vaccine 
Tlierapy. 



nation. 



536 INFECTION AND IMMUNITY. 

Keports regarding the curative injection of 
streptococci have been conflicting. It has been 
found that the use of galactose as a means of kill- 
ing the streptococci results in a better preservation 
of antigenic properties than does the use of heat. 

Weaver concludes that the use of therapeutic 
injections of galactose-killed streptococci is of 
value only in subacute and chronic streptococcus 
infections. 
Agg-ipti- The agglutinability of streptococci from differ- 
ent sources, and even from the same source, varies 
a great deal. Also the normal serums of man and 
animals have a variable agglutinating power for 
different strains of streptococci. By immunization 
with a given strain the agglutinating power is in- 
creased, but not uniformly for all strains. Com- 
monly the strain used for immunization is agglu- 
tinated more strongly than heterologous strains, 
the latter sometimes undergoing no agglutination 
whatever. These variations do not depend on dis- 
coverable differences in the cocci or the diseases 
which they produce. A given antistreptococcus 
serum does not agglutinate equally all streptococci 
from cases of scarlet fever (Weaver). Also strep- 
tococci vary greatly in their ability to stimulate 
to the formation of agglutinins. On the whole 
those which produce long chains are more suscep- 
tible to agglutination and yield stronger serums 
than those with short chains (Aronson, Tavel, 
v. Lingelsheim). By passage the agglutinating 
properties undergo rather complex changes. The 
organism then produces a stronger agglutinating 
serum and is agglutinated more readily by this 
serum than the same strain which had not been 



AGGLUTINATION. 537 

passed through animals. If passage is discon- 
tinued it reverts to its former condition. 

The variations are such that the agglutination 
reaction is of little or no value in differentiating 
different types of streptococci. 

As to the clinical value of the test for the diag- 
nosis of scarlet fever, the conclusions of Weaver 
may be cited : 

1. Of streptococci cultivated from cases of scar- 
latina, some are agglutinated by almost all scar- 
latinal sera, but at dilutions varying from 1/60 
to 1/4000; others are agglutinated by the same 
sera with less constancy and at lower dilutions, and 
many are not agglutinated at all. 

2. Streptococci cultivated from cases of scar- 
latina are agglutinated by sera from cases of lobar 
pneumonia and erysipelas at about the same dilu- 
tions as by scarlatinal sera, and in the case of ery- 
sipelas even at higher dilutions. 

3. The same appears to be true of typhoid fever 
serum, so far as limited tests indicate, and to al- 
most the same extent of puerperal-fever serum. 

4. The agglutination reaction between the 
streptococci cultivated from cases of scarlatina and 
the serum from cases of scarlet fever is in no way 
specific, and can not be of any value as a means of 
diagnosis. 

By growing streptococci on a medium which 
contains serum (serum bouillon), they form fewer 
and shorter chains and are better suited for ag- 
glutination tests. 

III. STAPHYLOCOCCI. 

Staphylococci are spherical cells from 0.7 to 0.9 
microns in diameter, typicalfy, and by light stain- 






538 INFECTION AND IMMUNITY. 

ing are often seen to consist of two hemispheres, 
which are separated by a delicate cleft. In pus 
they are found in small groups of two to nine or 
ten, ocasionally as diplococci, tetrads or very short 
chains. 
c S 1 Bi V i ti< l u They are luxuriant growers on nearly all media 
properties, which are suitable for bacteria, preferring, how- 
ever, a slightly alkaline reaction. Growth is best 
in the presence of oxygen, but proliferation occurs 
in its absence. Sputum, serum and ascitic fluid 
are favorable media, and in the last two the cocci 
may be agglutinated. An alkaline reaction is pro- 
duced in litmus milk, and the casein is precipitated 
and partly digested. The production of a proteo- 
lytic ferment is shown by liquefaction of gelatin 
and the formation of a clear zone about the colo- 
Ferments. n i es w hen grown in plates which contain coagulat- 
ed serum (Loeb, cited by Neisser and Lipstein). 
Albumin is changed into peptone. Loeb distin- 
guishes between a ferment which liquefies gelatin 
(gelatinase, a "collolytic" ferment), and one which 
digests albumen (tryptic ferment). Gelatinase is 
present in staphylococcus filtrates and normal 
serums are rich in antibodies for it. A fat-splitting 
ferment (lab ferment) is also present in the 
filtrates. The fact that the pus which is produced 
in staphylococcus infection does not coagulate may 
be due to the action of the proteolytic ferment, 
which digests the fibrinogen. 
staphjio- Van der Yelde had noted in 1894 that "staphy- 
lotoxin" (staphylococcus filtrates) cause hemoly- 
sis. Neisser and Wechsberg, in 1901, by growing 
the organisms in bouillon of suitable alkalinity, 
obtained hemolytic filtrates, giving the name of 
staphylolysin to the hemolytic principle. The hemo- 



lysin. 



LEUCOCIDIN. 539 

lytic action of the staphylococcus is readily seen 
in cultures on blood-agar plates; a zone of hemo- 
Lysis forms about the colonies. Erythrocytes of the 
rabbit, when placed in bouillon cultures, undergo 
hemolysis. Staphylotoxin also produces hemolysis 
in the living body. The maximum production of 
staphylolysin occurs after a growth of nine to 
fourteen days in alkaline bouillon, and nearly 
all pathogenic strains yield it, whether aureus, 
albus or citreus. It is not formed by non-patho- 
genic strains. The toxin is destroyed by exposure 
to a temperature of 56° C. for twenty minutes. A 
specific antitoxin is present in many normal 
serums and may be increased by immunization 
with the toxin or the living organisms. 

In 1894 van der Velde found in the pleural Lencocidm. 
exudates caused by inoculation with killed cultures 
of the staphylococcus a substance which is toxic 
for leucocytes, causing them to swell and the nuclei 
to disappear. This substance is called leucocidin. 
It is also produced in culture media, but the ability 
to form it is not so widely distributed as in the 
case of the hemolysin. Leucocidin is a true toxin, 
like the hemolysin; most normal serums contain 
antileucocidin, and the latter is increased by im- 
munization with the toxin. 2 The suggestion is a 
natural one that leucocidin may be a factor in 
combating phagocytosis in infections with the 
staphylococcus. Neisser and Wechsberg de- 
vised a "bioscopic method" of determining the 
cytocidal action of the toxin. Living leucocytes, 
like other living cells, have the power of decoloriz- 
ing methylene blue when oxygen is excluded. The 

2. Leucocidin and staphylolysin will not yield antitoxins 
when their activity has been destroyed by heat. 



INFECTION AND IMMUNITY. 



Toxic 
Filtrates. 



Endotoxin. 



"V arieties of 
Staphylo- 
coccus. 



destructive action of the toxin on the leucocytes 
is indicated by the failure of this reduction when 
the toxin is mixed with the cells. 

Old culture nitrates (two to three weeks) show 
a rather high degree of toxicity for animals, pro- 
ducing extensive degeneration of the convoluted 
tubules in the kidne}^ a degeneration which is 
somewhat selective; hemorrhages into the in- 
testinal mucosa; degeneration of the ganglionic 
cells, and fever. According to Levaditi, a mast- 
cell leucocytosis develops. The nature of the fever- 
producing substance is unknown. The toxicity of 
filtrates is said to be destroyed by a temperature 
of 56° C. 

Cultures of the staphylococcus killed by heat 
show little toxicity, hence the question of the ex- 
istence of an endotoxin is on no better basis than 
in relation to the streptococcus. It is possible that 
the heat required to kill the organisms destroys the 
endotoxin as well as the soluble toxins mentioned 
above. The virulence of the organisms has no 
direct relationship to the hemolysin or leucocidin, 
or the toxicity of the filtrates. Very pathogenic 
strains may produce a filtrate of little or no 
toxicity. It seems then that the essential patho- 
genic agent of the organism is unknown; as in 
the case of the streptococcus, its infectiousness 
depends on its ability to resist the antibacterial 
activities of the body (phagocytic and digestive 
power of the leucocytes and opsonins). The part 
played by the leucocidin in this resistance is not 
definitely known. 

The many varieties of the staphylococcus are 
differentiated on the basis of pathogenicity, pig- 
ment formation, liquefaction or non-liquefaction 



STAPHYLOCOCCUS. 5-U 

of gelatin, and other cultural properties. The 
Staphylococcus albus differs from the Staphylo- 
coccus aureus only in its inability to form pig- 
ment, and it cannot be made to acquire this prop- 
erty. Pigment is formed most abundantly on 
potato, whereas little is formed on blood serum. 
Other pigment-forming varieties are: S. cereus 
flavus, S. pyogenes citreus, S. scarlatinus and 
Micrococcus hematodes. The S. epidermidis albus 
of Welch is of low virulence. Weichselbaum 
obtained a S. endocardititis rugatus from a case 
of endocarditis. Not all of these varieties produce 
soluble toxins. The pigment of 8. aureus is an 
excretion product which is formed only in the 
presence of oxygen. It is insoluble in water, sol- 
uble in alcohol and ether, and gives the reaction 
of a lipochrome (i. e., the pigment may be saponi- 
fied and gives the lipocyanin reaction in which the 
pigment turns blue when treated with concentra- 
ted sulphuric acid). 

Aside from wide individual variations, the re- Resistance 
sistance of staphylococci to heat depends on the 
concentration of the suspension, the nature of the 
medium (whether water, gelatin or pus), and 
whether the test is a dry or wet one (Neisser and 
Lipstein). Eighty degrees centigrade for one-half 
to one hour kills them under all conditions, and 
60° C. for one-half hour kills many strains when 
suspended in bouillon. They are not killed by re- 
peated freezing and thawing, and are very resist- 
ant to desiccation. When in the form of fine dust 
they die in twenty-eight days (Kirstein). Eesist- 
ance to the action of sunlight is variable; some 
strains are killed in from three to five hours. 



of Cocci. 



542 



INFECTION AND IMMUNITY. 



Staphylococci have f airly high resistance to anti- 
septics; when dried, corrosive sublimate (1/1000) 
kills them in two to three hours, and when im- 
bedded in pus from thirteen to sixteen hours are 
required (Ottavino). Methyl alcohol, tincture of 
green soap and methyl violet are relatively good 
disinfectants. Methyl violet in a dilution of 
1/10,000 kills them in from five to fifteen minutes 
(Stilling). Formalin readily hinders develop- 
ment, but its bactericidal power is low. It is 
difficult or impossible to sterilize wounds infected 
with the staphylococcus by means of antiseptics. 

Staphylococci are very widely distributed in na- 
ture and are to be found constantly in the super- 
ficial layers of the epidermis (S. epidermidis al- 
bus). 

In infections the staphylococcus attracts large 
numbers of leucocytes, and the pus does not coagu- 
late. The substance which attracts leucocytes is 
heat-resistant, since killed cultures will cause 
abscesses. In all but the most superficial lesions 
a characteristic result of infection is that of cell 
necrosis and the liquefaction of tissues. Neisser 
and Lipstein state that the necrotizing substance 
is a soluble toxin, since culture filtrates cause 
marked necrosis of the internal organs when in- 
jected (liver, heart, kidney). "Hence in staphylo- 
nrycosis we can distinguish two active substances 
(v. Lingelsheim) , the leucotactic substance in the 
bodies of the cocci and the more important soluble 
staplrylotoxin which exercises not only a local but 
also a general toxic action on the body'' (Neisser 
and Lipstein). 
Amyloid Davidson produced amyloid degeneration in 
ation. rabbits and mice by the injection of living cultures. 



Leucotactic 
and Necrotiz- 
ing Sub- 

tances. 



STAPHYLOCOCCUS INFECTIONS. 



543 



Suscepti- 
bility of 

Animals. 



This was confirmed by Lubarsch, who found the 
condition most readily produced in the chicken 
and with more difficulty in the mouse, rabbit and 
dog. It rarely results if suppuration is avoided. 
Killed cultures may be used. 

Babbits and mice are the most susceptible ani- 
mals. The susceptibility of man is much greater. 
The organisms are most virulent for rabbits when 
injected intravenously, and a variety of lesions 
may result, as abscesses in various parts of the 
body (especially the kidney, heart and muscles), 
arthritis, endocarditis, etc. They are less patho- 
genic when injected into the pleural or peritoneal 
cavities. Babbits are rarely to be infected by the 
feeding of cultures. In experimental infections 
degenerations of the axis cylinders in the white 
and gray matter, and of ganglionic cells, have been 
noted. The virulence of staphylococci is subject 
to great variations, and it may be increased by 
passage. In passing a culture through the rabbit 
eight times, v. Lingelsheim reduced the fatal dose 
for rabbits from 5 c.c. of a 24-hour broth culture, 
to 1/100 c.c, but a corresponding increase in viru- 
lence for the mouse and guinea-pig did not occur. 
Virulence for animals is not a reliable index of 
virulence for man. 

The staphylococcus is the most common pus infections 
producer in man. The most frequent infections 
are those of the skin, the organisms gaining en- 
trance through the hair follicles rather than 
through the sweat ducts (Unna), resulting in such 
conditions as acne pustules, abscess of the skin 
and subcutaneous tissue, furuncles and carbun- skin. 
cles. They are found almost constantly in the 
lesions of impetigo and often in pure culture. 
They have been much vaunted as a cause of 



Mucous 
Surfaces. 



Septicemia. 



Serous Sur- 
faces and 
Bones. 






544 INFECTION AND IMMUNITY. 

eczema and they may be important as a secondary 
agent in this condition. The ordinary eczema prob- 
ably is not parasitic in its cause, however (Sabou- 
raud), and Neisser and Lipstein dispute the claim 
of Bender and others that eczema produced by 
staphylococcus filtrates is due to products of the 
microbe. This conclusion was justified, since the 
same results were obtained with pure bouillon of 
similar alkalinity, the property could not be de- 
stroyed by heat, and antistaphylococcus serum was 
not able to prevent the dermatitis. Furuncles may 
be produced by rubbing virulent cultures into the 
skin, and abscesses by the injection of minute 
amounts. The staphylococcus causes purulent or 
seropurulent conjunctivitis rather infrequently. 
Primary infections of cavities which communicate 
with the surface, as the antrum of Highmore, the 
middle ear, nose, bronchi, lungs and tuberculous 
cavities, are not uncommon, and mixed infections 
with the staphylococcus in these localities is the 
rule, regardless of the primary cause. Infection 
of the mucous surfaces is less common than of the 
skin, however. It rarely causes aphthous inflam- 
mations, anginas, pneumonia, enteritis and cys* 
titis when unmixed with other organisms. 

Staphylococcus septicemia of great virulence oc- 
casionally follows primary infection in other parts 
of the body, as wound infections, tonsillitis, puer- 
peral infection (rare) and the so-called malignant 
carbuncles of the upper lip. In such instances a 
thrombophlebitis may be the means by which the 
organisms are poured into the circulation in large 
numbers. Inflammations of the serous surfaces, 
as the pleura, peritoneum and endocardium, are 
rarely primary, but follow systemic infection; the 



IMMUNITY TO STAPHYLOCOCCUS. 545 

endocarditis usually is ulcerative and leads to 
metastatic foci of infection. Staphylococci have a 
particular affinity for the bony tissues, especially, 
the bone marrow and the periosteum; they are the 
most common agent in the production of osteomye- 
litis and cause the so-called periostitis albuminosa. 
It is thought that they may persist in bone lesions 
for a period of years and later start up a fresh 
process. They involve the joints less frequently, 
but have been found, presumably as secondary 
agents, in acute rheumatism, and as the primary 
cause in pyemic abscesses of the joints. They are 
found occasionally in abscesses of the mammary 
and parotid glands, liver, lungs, and in pyorrhea Mixed 
alveolaris (rare). The cultivation of staphylococci 
in a pure state from the tissues does not of neces- 
sity indicate that they are the essential organism 
in the process (smallpox, rheumatism, etc.). Pre- 
vious infections by many organisms, and likewise 
traumas, predispose to localization of the staphy- 
lococcus, and any infectious process in the skin is 
likely to be invaded by these organisms secondarily. 

Infections with the staphylococcus are charac- Leucocytes 
terized by both local and general leucocytosis, the immunity. 
local leucocytosis being a part of the suppurative 
process. As stated above, the staphylococcus con- 
tains a thermostabile constituent, which exerts a 
positive chemotatic effect on the leucocytes. Al- 
though it is possible to consider the accumulation 
of the leucocytes merely as the expression of this 
affinity, it has been shown with sufficient clearness 
that polymorphonuclear leucocytes are able to in- 
gest living staphylococci and kill them. 3 They 

3. Phagocytosis of staphylococci was first observed by 
Kirch in 1889. 



546 INFECTION AND IMMUNITY. 

may be found within the leucocytes in both natural 
and experimental infections.- When injected into 
the pleural or peritoneal cavity of the guinea-pig 
phagocytosis is well begun within one-half hour 
and reaches its height in four to five hours. 
Bactericidal Experiments which were begun by van der Velde 

oocytes and in 1894 demonstrate the bactericidal action of leu- 
SSes! cocytic exudates. The action is not so strong in 
the cell-free exudate as when the leucocytes are 
present, and when the leucocytes are caused to dis- 
integrate by some means, as by alternate freezing 
and thawing, trituration, the action of leucocidin, 
or treatment with distilled water, the bactericidal 
power of the fluid is increased. Presumably the 
leucocytes discharge their bactericidal contents into 
the surrounding fluid as a result of such inju- 
ries. The nature of the bactericidal substance is 
not known exactly; from the fact, however, that 
leucocytes contain complement it has been suggest- 
ed that they discharge this complement which then 
acts with amboceptors in the serum in destroying 
the organisms. It is possible that the cocci before 
they are taken up by the leucocytes have absorbed 
amboceptors and after their ingestion are suscepti- 
ble to the action of the endocellular complement. 
In contrast to the distinct bactericidal power of the 
leucocytes stands the very low or entire absence of 
a similar action by both normal and immune 
serums. It would seem, then, that the most power- 
ful agency in natural resistance to invasion by the 
staphylococcus is represented in the phagocytic 
and bactericidal activities of the leucocytes. Opso- 
nins are essential for phagocytosis. 
Active-jm- In 1888, Eichet and Hericourt showed that it 

mumzation. ^ ag p^g^^ t j ncrease the resistance of the rabbit 



IMMUNIZATION. 



547 



against the staphylococcus by immunization with 
pure cultures. 4 

One may immunize either with living or killed 
cultures or with culture filtrates. Immunization 
with the bacterial cells must proceed slowly in 
order to avoid killing the animals. When filtrates 
containing leucocidin or staphylolysin (hemolysin) 
are used, antitoxins for these substances are 
formed. The antistaphylolysin obtained for one 
strain neutralizes the hemolysin of all strains. 
The most prolonged immunization with bacterial 
cells causes no appreciable increase in bacterioly- 
sins. 

The serum of one who has recovered from a Protection 
staphylococcus infection, or that of immunized an- senJn^. un ' 
imals, is protective for other animals; 0.1 to 0.2 
c.c. of an immune serum given subcutaneously 
protected mice from a fatal dose of cocci given 
two hours later, whereas other mice were killed in 
from 8 to 12 hours. When the serum was given 
24 hours in advance of the culture, from 0.02 to 
' 0.03 c.c. saved them (v. Lingelsheim, cited by 
Neisser) . The results of Petersen and of Proscher 
were similar. In spite of this rather strong pro- 
tective action, immune serums have little or no 
curative power. 

No clearer explanation of the action of the im- 
mune serum is given than that afforded by the 
experiments of Proscher, who injected guinea- 
pigs, rabbits and mice with normal and immune 
serums and followed this 24 hours later with in- 
oculation of the cocci into the peritoneal cavity. 



Properties 
of Serums. 



4. Their experiments in protecting and curing other ani- 
mals with antistaphylococcus serum represent the first at- 
tempt made in the direction of passive immunization. 



548 INFECTION AND IMMUNITY. 

Thirty minutes after injection of the cocci the 
exudate in all animals showed an enormous leuco- 
cytosis. At first they were chiefly mononuclears, 
but later gave place to polynuclears. In the ani- 
mals which had received the immune serum, mas- 
sive phagocytosis had occurred, and in the course 
of an hour very few cocci were extracellular. On 
the other hand, practically no phagocytosis had 
taken place in the animals which had received the 
normal serum (cited by Neisser). Virulent 
staphylococci were taken up less readily than 
avirulent. Such results suggest that the protective 
power of the serum is due to its ability to stimulate 
phagocytosis, and this in turn depends on the 
increased quantity of bacteriotropic substances 
formed in the serum as the result of immunization 
(Wright and others). 
vaccination. In the hands of Wright, vaccination with killed 
cultures of the staphylococcus has been very suc- 
cessful in the cure of obstinate cases of acne, fu- 
runculosis and many other chronic staphylococcus 
infections. Bouillon cultures are grown for three * 
weeks and then killed by exposure to a tempera- 
ture of 60° C. for an hour. In order to control 
dosage, the vaccine is standardized by estimating 
the number of bacilli in each cubic centimeter. 
This is done by mixing equal quantities of the 
vaccine with normal blood, and, after staining a 
preparation on a slide, determining the ratio of 
cocci to erythrocytes. There being about 5,000.000 
erythrocytes to the cubic millimeter in normal 
blood, the number of cocci is readily reckoned 
from the ratio which was found. From 2,500 
millions to 7,500 millions of cocci may be given 
in an injection. The quantity to be used is 






OPSONIC INDEX. 



549 



determined by the effect which an injection has on 
the opsonic content of the patient's serum. If a 
suitable dose has been given, there occurs a short 
negative phase in which the opsonins are decreased 
in quantity, and this is followed by a rather pro- 
longed positive phase when they undergo an in- 
crease. If too large a dose is given, the negative 
phase is exaggerated and prolonged. In many in- 
stances it has been noted that improvement and 
recovery go hand in hand with an increase in the 
opsonins. As in streptococcus infections the total 
resisting power of the body depends on the varia- 
tion in the capability of the leucocytes to take up 
and digest cocci as well as the opsonic action of 
the serum. 

The normal serums of man and many animals 
may agglutinate the staphylococcus, but with no 
constancy. In one instance human serum aggluti- 
nated in a dilution of 1-100 (Kraus and Low), 
and normal goat serum in a dilution of from 
1-50 to 1-400 (Amberger, cited by Neisser). The 
serums from cases of staphylococcus infection 
(e. g., osteomyelitis) and of highly immunized an- 
imals undergo an increase in the quantity of ag- 
glutinins. The agglutination usually is strongest 
for the homologous strain, and if other strains are 
agglutinated equally it signifies a close relation- 
ship to the homologous strain. 

From the fact that only pathogenic strains pro- 
duce hemolysin and leucocidin, Neisser and 
Wechsberg considered them specifically different 
from non-pathogenic strains. This view is borne 
out by the results obtained with the agglutination 
test. Serums obtained by immunization with 
pathogenic strains have a much higher aggluti- 



"Opsonic 
Index." 



Aggluti- 
nation. 



550 INFECTION AND IMMUNITY. 

nating power for these strains than for non-patho- 
genic varieties, and the converse is also true. There 
are, however, many variations in the agglutinabil- 
ity of the members in each group, a fact which in- 
dicates variations in the receptor complex of the 
different strains. It has been suggested that a 
polyvalent serum obtained by immunization with 
a sufficient variety of pathogenic strains will be 
efficient in differentiating the latter from non- 
pathogenic varieties by means of the agglutina- 
tion test. 

Wright, noting an increase in the agglutinating 
power when patients are treated by his method, 
considers that this increase is an index of the im- 
munity which is established. 

IV. MICROCOCCUS CATARRHALIS. 

For some years diplococci resembling the gono- 
coccus and the meningococcus morphologically and 
in staining reactions have been found in the spu- 
tum by a number of observers, and to this coccus 
Pfeiffer gave the name of Micrococcus catarrhalis. 
It is frequently found in the respiratory passages 
in influenza-like infections and other inflamma- 
tory conditions, and occasionally in lobular pneu- 
monia. It may be associated with the influenza 
bacillus or the pneumococcus. Among 140 cases 
of diseases of the respiratory passages Ghon and H. 
Pfeiffer found it 81 times, and M. Neisser demon- 
strated it in 16 cases of whooping-cough, in 
one of measles and scarlet fever, and in 
two of diphtheria. It loses significance in relation 
to these diseases, however, since Jundell found it 
frequently in the mucus of the normal trachea, 
and Weichselbaum cultivated it frequently from 



GOKOCOCCUS. 



551 



the healthy nasal fossa?. According to Ghon, 
Pfeiffer and Sederl, ''Micrococcus catarrhalis, 
without the association of other microbes, is able 
to cause bronchitis and pneumonia with the clini- 
cal type of pneumonia due to the pneumococcus. 
The symptoms caused by the Micrococcus catarrh- 
alis do not form a clinical type. They resemble 
infections by the pneumococcus or the bacillus of 
Pfeiffer (Influenza)" (cited by Bezancon and de 
Jong). Others are not so positive concerning the 
pathogenic properties of the organism. Its etio- 
logic role is not yet well established. It has little 
pathogenicity for animals, although peritoneal and 
pleural infection is possible in guinea-pigs. 

It differs from the gonococcus and meningococ- 
cus in certain cultural characters. 



V. GONORRHEA AND OTHER INFECTIONS WITH THE 
GONOCOCCUS. 

A. Neisser discovered the gonococcus in 1879, The Gono- 
cultivated it in 1884, and demonstrated its specific coccus - 
relation to gonorrhea by the inoculation of pure 
cultures into the human urethra. It is a diplo- 
coccus, young pairs having a figure-of-eight con- 
tour, whereas older pairs show a typical biscuit 
or coffee-bean shape. The organism is non-motile, 
has no flagella and forms no spores. It can be 
cultivated only on media which contain serum, 
ascitic or a similar fluid. Its failure to stain by 
Gram's method is of great diagnostic importance 
in the examination of urethral discharges; other 
organisms resembling the gonococcus are found in 
the urethra and vagina with great rarity. The 
reaction loses its differential value in the examina- 
tion of secretions of the nose, mouth, and, to some 






Cultivation 
and Resist- 



552 INFECTION AND IMMUNITY. 

extent, of the conjunctiva, where the meningococ- 
cus and the Micrococcus catarrhalis may be en- 
countered. 
Phagocytosis. In the purulent stage of a gonorrheal infection 
the cocci are found almost entirely within the leu- 
cocytes, whereas in earlier stages, when the dis- 
charge is slight and of a mucous character, and 
also during convalescence, when the secretion 
again becomes mucous, they are largely extracel- 
lular. They are never within the nuclei. The 
process is one of active phagocytosis in which the 
cocci play a passive role. They occur not only on 
the surface of the epithelium, but penetrate be- 
tween and beneath the epithelial cells, and even 
into the a'djacent connective tissue. 

In culture media growth is slow and scant, and 
cultures rarely live longer than one or two weeks, 
unless they are transplanted to suitable fresh media. 
On the latter they may be carried through many 
generations without losing their virulence. When 
dried they die very quickly, but may live for some 
hours on linen (towels) or the skin, and for 
twenty-four hours in warm water. They are very 
susceptible to temperatures above 42° or 43° C. 
and show very little resistance to antiseptics, par- 
ticularly the silver salts. 
Toxicity and The gonococcus secretes no soluble toxin, but 
lmience. con £ a i ns an endotoxin or toxic "protein" which 
causes local and general symptoms in both man 
and animals. Dead cultures produce an inflamma- 
tory exudate in the peritoneal cavity of guinea- 
pigs and mice, resulting in death if the dose is 
sufficiently large, and when injected into the 
urethra of man a temporary inflammation results. 
An actual infection of any sort can not be pro- 



GONOCOCCUS. 



553 



duced in animals; the cocci are killed without be- 
ing permitted to proliferate. The endotoxin (gon- 
otoxin) is fairly resistant to heat, being destroyed 
only after prolonged exposure to a temperature of 
100° C. 

In man the mucous membranes and endothelial 
surfaces are more susceptible to infection than 
other tissues. The urethra of male and female at 
all ages, the conjunctiva in the new-born, the 
vagina, uterus and tubes are probably the most 
susceptible. Less susceptible are the vagina in 
older women, especially those who have borne chil- 
dren, the bladder and, in adults, the conjunctiva. 
It is remarkable that there are so few cases of 
gonorrheal ophthalmia in adults, considering the 
opportunities for infection. Infection of the 
mouth, nose and tear sacs is extremely rare. Ex- 
tension from the urethra to adjacent structures 
takes place either by way of the surfaces, as in 
involvement of the prostate, epididymis, glands of 
Bartholin, uterus, tubes, ovaries, peritoneum, blad- 
der and kidneys, or by way of the lymphatics as in 
infections of the periurethral tissue or cellular tis- 
sue of the pelvis. Usually infections of the bladder 
and kidney, and not infrequently of the prostate, 
Fallopian tubes and pelvic tissue are of a mixed 
character (staphylococcus, streptococcus), but not 
necessarily so. Arthritis, tendovaginitis, endocar- 
ditis, which usually is vegetative but may be ulcer- 
ative, are the more common metastatic complica- 
tions. Less frequent are pericarditis, pleuritis, 
subcutaneous abscesses and iritis. As to whether 
the cutaneous phenomena sometimes seen are due 
to metastases or are of purely toxic origin seems to 
be undetermined. The blood stream may be in- 



susceptible 

Tissues. 



Changes. 



554 INFECTION AND IMMUNITY. 

fected by way of the lymphatics or local blood 
vessels (gonorrheal thrombosis). 

The influence of the enormous phagocytosis of 
the cocci on the course of gonorrhea is unknown. 
Since the ingested cocci usually have a typical 
form and stain well, it would seem that they resist 
the action of the leucocytic ferments. Likewise 
the nuclei of the leucocytes usually stain well, 
hence there is no evidence of a marked toxicity 
of the cocci for these cells. The mechanical im- 
prisonment of the organisms by the leucocytes 
may be of influence in localizing the infection. 

urethral During the course of gonorrhea "there takes 
place a pronounced metaplasia of the epithelium 
in which the cylindrical cells are changed into a 
more cuboidal and even pavement form." Follow- 
ing this change the gonococci are limited to the 
surface of the altered epithelium and penetrate 
more deeply only in the vicinity of the glands and 
crypts. "Eventually the gonorrheal process is 
limited to such isolaled points and the gonorrhea 
thereby enters into a chronic stage" (observations 
of Finger, cited by ISTeisser and Scholtz). 

chronic The conditions which cause the subsidence of 
acute gonorrhea and allow it to persist as a chronic 
infection have been the subject of much specula- 
tion, unproductive for the most part. It is not 
due to a decrease in the virulence of the cocci 
since their original infectiousness is retained for 
others ; nor does the local resistance of the mucous 
membrane reach a high point, since reinfection, 
or better "superinfection" is possible at any time. 
A man suffering from chronic gonorrhea and 
having infected his wife, may again be infected 
by his wife when the gonorrhea of the latter has 



Gonorrhea. 




GONOCOCCUS SERUM. 555 

become subacute or chronic. It has been suggested 
that the condition in chronic gonorrhea may be 
one of "mutual habituation between the mucous 
membrane and the gonococcus," i. e., a habituation 
between this particular mucous membrane and 
this particular gonococcus. Because of prolonged 
existence under unvarying conditions, the growth 
energy of the organism may have become less, 
whereas, if it is placed in a slightly different me- 
dium (transference to another individual), its 
growth energy (ability to proliferate), becomes 
augmented, and reinfection of the original host 
with the same strain becomes possible. 

It has often been noted that subsequent attacks 
run a milder course than the primary infection, 
but susceptibility is always present. 

Menclez, Calvino, and also de Christmas have immwity. 
immunized with the coccus or toxic substances 
prepared from it. By growing the organism in 
serum bouillon de Christmas prepared a toxin, 
the toxicity of which was tested by intracerebral 
injections in the guinea-pig. Immunization of 
the guinea-pig resulted in a serum with antitoxic 
properties. Corroborative work has not been pub- 
properties. Torrey has shown that by immuniza- 
tion of animals a serum may readily be produced 
which contains specific bacteriolysins, agglutinins, 
precipitins and complement deviation antibodies. 
Hamilton and others have found that in gonor- 
rheal vulvovaginitis the opsonic index is low in 
early stages and in those in which recovery does 
not take place, and becomes higher with recovery. 

Torrey in 1906 prepared an antigonococcus se™tiierapy 
serum by immunization of rabbits. Since that nation. 
time, a number of different serums have been pre- 



556 INFECTION AND IMMUNITY. 

pared from such animals as horses and rams. The 
reports concerning the value of antigonococcus 
serum have been as yet too varied to admit of a 
conclusion. 

The subcutaneous injection of dead gonococci 
for curative purposes has been apparently of little 
value in acute urethral infections. In chronic 
infections of the urethra, prostate and seminal vesi- 
cles some satisfactory results have been obtained. 
Cole and Meakins, and Irons find that the vaccine 
treatment of gonorrheal arthritis is of value in 
lessening the pain and in shortening the course of 
the infection. 

VI. EPIDEMIC CEREBROSPINAL MENINGITIS. 

Microbes Acute inflammation of the meninges may be 
Meningitis, caused by a number of micro-organisms: Micro- 
coccus meningitidis, also called the Diplococcus 
intracellularis meningitidis, or briefly the men- 
ingococcus; Diplococcus pneumonice; Streptococ- 
cus pyogenes; Staphylococcus pyogenes; Bacillus 
influe?izo3; Bacillus pneumoniae; Bacillus typho- 
sus; Bacillus coli communis; Bacillus mallei; Ba- 
cillus pestis. The first two of this number, the 
meningococcus and the" pneumococcus, in addition 
to causing sporadic cases, also produce more or 
less extensive epidemics of so-called primary men- 
ingitis. That the pneumococcus may also cause 
meningitis secondary to pneumococcus infections 
in other parts of the body has been mentioned. 
Also the meningitis caused by the other pyogenic 
cocci usually is secondary to some other suppura- 
tive focus, often the middle ear; that caused by 
the organisms of typhoid, glanders, plague and 



MENINGOCOCCUS. 557 

influenza occurs during the course of the diseases 
caused by the corresponding micro-organisms. 

Previous to 1887 diplococci resembling the pneu- Micrococcus 
mococcus had been found in the exudate in cases 
of cerebrospinal meningitis by Foa and Bordoni- 
Uffreduzzi, by Fraenkel and others. Weichsel- 
baum made similar observations during the same 
year, and in addition described six cases in which 
a diplococcus of another nature was present in 
pure cultures. To the latter he gave the name of 
Diplococcus intracellularis meningitidis. Exten- 
sive observations by others, both in Europe and 
America (Councilman, Mallory and Wright, and 
others), revealed the presence of the last-named 
organism in many instances, and showed that it is 
the most common cause of epidemic cerebrospinal 
meningitis. 

The meningococcus resembles the gonococcus 
closely in that it is usually found in biscuit-shaped 
pairs, nearly always within pus cells, and does not 
stain by Gram's method (Weichselbaum). It is 
properly to be called a micrococcus since it divides 
in two transverse directions (Albrecht and Ghon) ; 
tetrads, small groups and short chains are some- 
times seen. However, it forms no striking chains, 
is non-motile and produces no spores. Growth 
may be obtained on some of the ordinary media 
(glycerin agar), in which the organism differs 
from the gonococcus, but a medium which contains 
blood or serum is much more favorable. It is an 
obligate aerobe, grows best at the body tempera- 
ture and virulence is soon lost under artificial 
conditions. 

It produces a membrane on meat broth with viability. 
clouding of the medium. Viability is retained 



558 



INFECTION AND IMMUNITY. 



Virulence; 
Endotoxin. 






only for a few days at room temperature. When 
dried on paper and exposed to the sunlight it lives 
no longer than twenty-four hours, in a dark room 
seventy-two hours (Councilman, Mallory and 
Wright). It is killed by a temperature of 65° C. 
for thirty minutes (Albrecht and Ghon). 

The meningococcus has little virulence for ani- 
mals. When injected in sufficient quantity into 
the peritoneal or pleural cavity of white mice 
death results in from twenty-four to forty-eight 
hours, but not when given subcutaneously. Men- 
ingitis may be produced by subdural injections, 
but the disease does not resemble the epidemic 
meningitis of man. So far as is known at present 
the organism does not produce a soluble toxin, but 

possesses rather an endotoxin. Although the dis- 
infection L 10 ■ ■ --x- 
Atria, ease is usually spoken of as a primary meningitis, 

there is reason to believe that it is secondary to an 
acute rhinitis or acute inflammation of the acces- 
sory sinuses or middle ear, in many instances. 
From these places the coccus may readily reach the 
meninges by way of the lymphatic channels, or 
blood. The latter, according to Elser and Hun- 
toon, is probably the usual route. It has been 
found repeatedly in the noses of those associated 
with patients with the disease; in such cases an 
acute rhinitis may be present without the subse- 
quent development of meningitis. The clinical his- 
tory shows that the infection commonly is preceded 
by acute rhinitis. The inflammation in the menin- 
ges is always cerebrospinal in its distribution and 
is characterized by a purulent or fibrino-purulent 
exudate in which the diplococci are present in 
varying quantities. Diagnosis may often be estab- 
lished clinically by the microscopic or cultural 



i 



MENINGITIS. 



Complica- 
tions and 
Other 
Infections. 



examination of the cerebrospinal fluid which is 
removed by lumbar puncture. 

Acute encephalitis, acute bronchitis, lobar pneu- 
monia and acute arthritis have been observed as 
complications, in which organisms resembling the 
meningococcus have been- found in a number of 
instances. An accompanying bronchitis, lobar or 
lobular pneumonia may be caused by mixed infec- 
tion with other organisms (pneumococcus, strepto- 
coccus, staphylococcus). Since it would be diffi- 
cult to explain some of these complications except 
on the basis of metastasis, it seems very probable 
that the organism reaches the blood stream. Micro- 
cocci resembling the meningococcus have been 
found in acute bronchitis, rhinitis, lobular pneu- 
monia and conjunctivitis, in the absence of cere- 
bral involvement, and it is possible that it may be 
the cause of independent inflammations in these 
tissues. Weichselbaum, however, is inclined to 
doubt the identity of such organisms with the 
meningococcus. Particularly in cases of bronchi- 
tis and lobular pneumonia the coccus may be con- 
fused with the Micrococcus catarrhalis of Pfeiffer, 
with which it is identical morphologically. 

The extent to which the meningococcus is a 
normal inhabitant of the nasal mucous membrane 
is unknown. 

Since the organism seems to be excreted chiefly Transmission 

° J and Con- 

or only with the nasal discharges, the latter prob- tagiousness. 

ably are important for transmission of the infec- 
tion. Because of the low resistance of the organ- 
ism to desiccation and light, transmission prob- 
ably is a fairly direct one. This is suggested also 
by the occasional occurrence of epidemics in insti- 
tutions. Contagiousness is of a rather low order; 



560 



INFECTION AND IMMUNITY. 



Suscepti- 
bility and 
Immunity. 



this is indicated by the distribution of the 111 
cases observed by Councilman. Mallory and 
Wright in Boston, the city being somewhat dif- 
fusely infected with very little tendency of the dis- 
ease to occur in groups of individuals or in several 
members of a family. 

The desirability of avoiding contact with the 
infected is evident; special prophylactic meas- 
ures are not known. In the presence of an epi- 
demic the treatment of rhinitis with local antisep- 
tics would suggest itself. 

Children and young people are particularly sus- 
ceptible to both epidemic and sporadic infections 
with the meningococcus. Exposure incident to the 
cold and variable weather of the winter and spring, 
in which seasons the disease prevails, may be in- 
fluential in lowering resistance. Second attacks 
are rare, Councilman, Mallory and Wright col- 
lecting only five such examples from the literature. 
Lipierre immunized animals with cultures and 
with a toxin, the latter being a glycerin extract of 
old cultures. Their resistance to infection was 
said to be increased, and the serum of highly im- 
munized animals was antitoxic, preventive and 
curative for other animals. Corroborative work 
is lacking. According to Davis, the serum in 
cases of epidemic meningitis shows an increased 
bactericidal power for the coccus on the thirteenth 
day of the disease; the agglutinins which develop 
probably persist for some time, but are little above 

Normal human serum is distinctly bactericidal 
toward the meningococcus. This property is 
increased in sera of meningitis cases, and is dimin- 
ished, but not entirely destroyed, by heating to 60° 
C. for thirty minutes. Cerebrospinal fluid acts in 
much the same way as heated serum. Normal 



MENINGITIS SERUM. 561 

cerebrospinal fluid does not contain opsonin for 
meningococci. 

In 1906, antimeningitis serum was prepared in semm 
this country by Flexner and in Germany by Kolle T,iera i>y- 
and Wassermann and Jochmann. The report of 
Kolle and Wassermann was the first to appear. It 
was quickly followed by that of Jochmann and 
later by that of Flexner. 

Flexner prepared his serum as follows : Horses 
were inoculated subcutaneously with one-fourth of 
a sheep's serum agar slant culture of meningococci 
which had been killed by heating to 60° C. for 
thirty minutes. The dose was doubled at each 
subsequent injection until an amount equal to 
four test-tube growths could be given at intervals 
of from five to seven clays. Alternate injections 
of living organisms and autolyzate of organisms 
were then given at seven-day intervals, in increas- 
ing doses until large quantities were given. The 
serum prepared in this way contains bacteriolytic 
amboceptors, opsonins, agglutinins and comple- 
ment-fixation antibodies. It has also an antitoxic 
action on toxic autolyzates of meningococci. 

Nearly all the above-named antibodies have been standard- 
used to estimate the therapeutic value of the 
serum. Jochmann, and Kolle and Wassermann 
estimated the strength of antimeningitis serum by 
the protection afforded mice and guinea-pigs 
against live meningococci. The method is unsatis- 
factory because of the difference of virulence of 
various strains of meningococci. Jobling con- 
cludes that the estimation of the dilution of the 
serum at which opsonic action is still present gives 
the best indication as to the value of the serum. 
"As a definite and suitable standard of strength 



562 



INFECTION AND IMMUNITY. 



a minimum dilution activity of a 1 to 5,000 dilu- 
tion of the antiserum is proposed." 
Action and Flexner and Jobling conclude from a study of 

Uses of the . ° . J . 

serum, the spinal fluid, that the most important action 
of the serum depends on bacteriolysis and 
increased phagocytic action. They give the follow- 
ing instructions for the use of the serum : 5 

"The antiserum should be kept in a refrigerator 
until it is to be used, when it should be warmed 
to the body temperature before it is injected. 

"The antiserum is to be introduced directly into 
the spinal canal after the withdrawal of cerebro- 
spinal fluid by means of lumbar puncture. 

"The quantity of antiserum to be used at a sin- 
gle injection should not exceed for the present 
30 c.c. It is desirable, although it would not 
appear essential, to withdraw from the spinal canal 
at least as much fluid as the amount of antiserum 
to be injected. The injection should be made 
slowly and carefully to avoid the production of 
s}<mptoms due to increased pressure. This pre- 
caution should be exercised especially where the 
quantity of cerebrospinal fluid withdrawn is less 
than the amount of antiserum to be injected. 

"The injection of the antiserum should be 
repeated every twenty-four hours for three or four 
days or longer. Whether any advantage will be 
gained by more frequent or more numerous injec- 
tions than here indicated a wider experience must 
decide. As much as 120 c.c. of the antiserum have 
been injected into the spinal canal in four days 
without causing unpleasant symptoms. 

"The evidence indicates that the earlier in the 
course of the disease the injections are made the 



5. Flexner, S., and Jobling, J. W. 
p. 190. 



Jour. Exp. Med., 1908, 



INFLUENZA. 563 

better the results. Hence, should the film prep- 
aration of the first fluid obtained by spinal punc- 
ture show Gram-negative diplococci, some of which 
are within leucocytes, an injection should be made 
immediately and without waiting for the results 
of culture tests. Should the diagnosis be left in 
doubt or the disease prove later to be of another 
nature than epidemic meningitis, no harm will be 
done by the injection of the antiserum. 

"Although the best results have thus far been 
obtained where the antiserum has been injected 
early in the disease, yet the serum should be used 
in its later stages also until our knowledge gov- 
erning the value of the serum becomes more pre- 
cise. The indications at present are that it is 
useless to employ the serum in the very late stages 
of the disease in which chronic hydrocephalus is 
already developed." 

Flexner and Jobling conclude from an analysis value of 
of a large number of reports of the use of anti- 
meningitis serum, that the serum is of value in 
reducing the period of illness and diminishing the 
fatalities due to the disease. The figures of Dunn 
show that in the Boston Children's Hospital, the 
mortality before the use of the serum, from 69 to 
80 per cent., was reduced to below 20 per cent, 
after the use of the serum. 

VII. INFLUENZA. 

Influenza occurs sporadically and in epidemics 
of greater or less proportions. Its extreme con- 
tagiousness is shown by the striking rapidity with 
which it spread over the whole civilized world in 
the epidemic of 1889 and 1890, leaving behind it 
a trail of lesser epidemics which have prevailed up 
to the present time. 



INFECTION AND IMMUNITY. 






Bacillus During the epidemic just cited a number of or- 

Inflnenza. l n -i n xi £. 

ganisms were erroneously described as the cause ot 
the disease. In 1892, however, Pfeiffer discovered 
a minute bacillus which he found constantly and 
in large numbers in the sputum of influenza pa- 
tients only. The observations of Pfeiffer have 
been confirmed by a large number of investigators, 
and the organism, Bacillus influenza, is now ac- 
cepted as the cause of the disease. It is one of the 
smallest of bacteria (0.2 or 0.3 by 0.5 microns), is 
non-motile and forms no spores. A medium con- 
taining blood or hemoglobin is essential for its 
artificial cultivation, and even under the best con- 
ditions it grows meagerly and slowly. A number 
of bloods, but particularly those of man and the 
pigeon, favor its growth. It is a strong aerobe. 
The organism is best stained by a dilute solution of 
carbol-fuchsin (1 to 10), and, like the plague 
bacillus, exhibits polar staining, i. e., the ends 
stain more deeply than the central portion. 
symbiosis. When the staphylococcus and some other organ- 
isms are grown in mixed culture with the influ- 
enza bacillus, the latter is stimulated to a more 
vigorous growth. According to Jacobsohn, killed 
cultures of the streptococcus greatly increase the 
virulence of the influenza bacillus when the mix- 
ture is injected into animals. 
Psendo- Pfeiffer designates as pseudoinfluenza bacilli a 
n BacniL number of influenza-like organisms which have 
been found in man and animals. They have the 
morphology of the influenza bacillus, are a little 
larger, and also prefer a medium which contains 
hemoglobin, but since some of them occur in ani- 
mals which are known not to be susceptible to in- 
fluenza, it is concluded that they can not be identi- 



INFLUENZA. 



565 



Resistance 
and 



cal with the influenza bacillus. The influenza-like 
bacillus which Jochmann and Krause consider as 
the cause of whooping-cough, may be mentioned 
in this connection. 

The resistance of the bacillus to desiccation, 
sunlight and unfavorable temperatures is very low. virulence 
It dies in from twenty-four to thirty-six hours at 
room temperature, when contained in sputum, and 
lives for about thirty-two hours in hydrant water 
(Pfeiffer). It is not highly virulent for animals, 
although a condition said to resemble influ- 
enza has been produced in monkeys by placing 
pure cultures on the nasal mucous membrane. 
Fatal infections may be produced by intra- 
venous inoculation of the bacillus into monkeys 
and rabbits, and killed cultures produce a fatal 
intoxication in rabbits. Virulent cultures in suffi- 
cient quantity produce fatal peritonitis in guinea- 
pigs. Since the bacilli seem not to proliferate 
when fatal quantities are injected intravenously 
into rabbits, and since fatal intoxication, without 
the occurrence of bacteriemia, may take place 
when a tracheal infection is induced in the ape 
(Pfeiffer), it is concluded that the toxic phenom- 
ena of influenza are due to the absorption of bac- 
terial toxins from the mucous surfaces. A soluble 
toxin has not been obtained in culture media. The 
organism is a facultative pus producer. 

So far as is known, the influenza bacillus is ex- 
creted only with the secretions of infected surfaces, 
i. e., from the upper respiratory passages, con- 
junctiva, ear, etc. The belief, commonly held, 
that the influenza bacillus does not enter the cir- 
culation probably is erroneous. That metastatic 
infection is possible, by way of the lymph or blood 



Distribution 
in the Body. 



566 



INFECTION AND IMMUNITY. 



channels, is shown by the occurrence of influenza 
meningitis, and, rarely, of influenza peritonitis 
(Hill and Fisch). According to Jehle, the influ- 
enza bacillus invades the blood very frequently in 
some of the acute exanthemata. It was found in 
the blood in 22 out of 48 cases of scarlet fever, in 
15 of 23 cases of measles, and in 5 of 9 cases of 
varicella (cited by Hektoen). Hence, these dis- 
eases would seem to create conditions favorable for 
evasion by this bacillus. When the bacilli reach 
the blood they probably are killed quickly. It is 
probable that the ordinary nervous phenomena of 
the disease are due to intoxication rather than to 
actual infection of the nervous structures. As to 
whether the symptoms of so-called intestinal in- 
fluenza are due to an invasion of the intestines 
by the bacilli or to a specialized action of circu- 
lating toxin seems not to have been definitely set- 
tled. There certainly is abundant opportunity for 
infection of the intestines in cases of bronchial 
influenza. In the bronchitis of influenza the or- 
ganisms are found in large numbers in the smaller 
bronchial tubes, both free and within leucocytes, 
hence, in searching for the bacilli clinically it 
should be certain that the sputum examined repre- 
sents the bronchial exudate. In influenza pneu- 
monia, which usually is of the lobular type, the 
bacilli, mixed with pus cells and contained in 
them, are found in large numbers in the alveoli. 
Pure cultures of the bacillus have been obtained 
from cases of conjunctivitis, and they occur not 
infrequently in middle-ear complications which 
develop during the course of the disease. Influ- 
. enza conjunctivitis sometimes occurs in epidemic 
form, particularly in institutions and schools. 



INFLUENZA. 



567 



Transmission, 
Infection 
Atria and 
Prophylaxis. 



Pneumonic foci which develop during influenza Mixed 
frequently show the pneumococcus, and sometimes 
the streptococcus or the bacillus of Friedlander in 
addition to the influenza bacillus, and similar 
mixed infections occur in pleurisy and in middle- 
ear diseases. Influenza may be superimposed on 
other infections; individuals suffering from pul- 
monary tuberculosis are particularly susceptible to 
influenza, and in them the prognosis is unfavor- 
able. 

The disease is transmitted directly from man to 
man and, chiefly, it is supposed, by means of in- 
fected droplets of sputum which are expelled in 
coughing and sneezing. Obviously kissing affords 
opportunity for infection. Infection by indirect 
contact is of less importance because of the rapid 
death of the bacillus after it leaves the body, but 
living germs may well be disseminated by soiled 
handkerchiefs or other contaminated linen. Dust 
infection possibly is of minor consequence. Chronic 
influenza in which the bacilli may persist in the 
bronchi for weeks, and cause recurrent acute at- 
tacks, is of importance for the maintenance of an 
epidemic. In tuberculous cavities the bacilli may 
flourish for long periods. 

Primary infection takes place in the upper res- 
pitory passages, and the disease extends readily 
from one surface to another, as from the nose to 
the pulmonary tissue. Infection of the ear usually 
is a complication of pharyngeal or pulmonary in- 
fection. Occasionally an influenza conjunctivitis 
is found without other localization. "Primary" 
infection of other organs, as the brain and perito- 
neum, are metastatic, although the original focus 
or atrium may not be observed. 



568 



INFECTION AND IMMUNITY. 



Immunity, 
Suscepti- 
bility and 

Recurrences. 



Little or nothing can be done in the way of 
general prophylaxis. Washing of the nose and 
mouth with antiseptics during an epidemic may 
reasonably be practiced, but with what success is 
uncertain. The aged and those of low vitality 
should avoid exposure to infection, for in them the 
severer complications, such as pneumonia, are 
more likely to occur. When influenza conjuncti- 
vitis appears epidemically in schools, the latter 
should be closed or the infected children excluded. 

Although little or nothing is known concerning 
the possibility of a natural immunity in man, ex- 
perience teaches that he is, on the whole, very sus- 
ceptible. The belief expressed by some that nurs- 
ing children are less susceptible than older people 
seems to have some foundation, although it is well . 
known that they are not entirely immune. Influ- 
enza is sometimes cited as an infection in which 
one attack creates a predisposition for a second, 
but the truth of this is doubted by many who have 
had extensive experience with the disease. Wutz- 
dorff, in a study of the epidemic which prevailed 
in Germany during 1891-92, finds in the small 
number of cases, the irregularity of their distribu- 
tion, and compartive exemption of rather large 
districts, reasons for believing that one attack con- 
fers a degree of acquired immunity; that is to say, 
the population had been so thoroughly infected 
during the preceding year or two that compara- 
tively few remained who were susceptible, although 
the disease itself appeared to be more malignant 
than in the previous year (cited from Beck). 
However, the occurrence of second attacks shortly 
after the first, and of repeated infections in some 
individuals indicate that acquired immunity is of 



Properties. 



SOFT CHANCRE. 569 

short duration. The aged, those of low vitality, 
and those with pulmonary tuberculosis, have low 
resistance to infection. 

Although Delius and Kolle were able to produce semm 
a slight increase m the resistance of -guinea-pigs 
by the intraperitoneal injection of cultures, noth- 
ing like a well-marked immunity was obtained; 
nor did the serum of immune animals or convales- 
cent man show increased protective power for 
other animals. Slatineano, however, obtained 
serum of some protective value for guinea-pigs, 
by the immunization of rabbits and guinea-pigs, 
but it had no curative effect. The results of Can- 
tani were similar, and both observers noted the de- 
velopment of bactericidal power, as determined by 
the Pfeiffer reaction, and of agglutinins. At pres- 
ent there seems little to hope from vaccination. 

There is said to be some increase in agglutinins 
in man as a consequence of infection. The agglu- 
tinating power of the serum of an immunized ani- 
mal may be as high as 1 to 500 (Cantani). 

VIII. SOFT CHANCRE. 

The independence of soft chancre and syphilis, 
and the infectiousness of the former by inoculation 
with the purulent secretions of the ulcers, were 
established long ago. Rollet found that filtered 
pus lost its infectiousness. 

A large number of observers had found bacteria Bacillus of 

. Ducreyi 

of one kind or another in the pus and in stained 
sections of the walls of the ulcers, and probably 
some of them (e. g., Unna), had seen the bacillus 
which Ducrey described (1889) and later culti- 
vated, and which is now proved to be the cause of 
the disease. The bacillus is very small (0.4x1.5 



570 INFECTION AND IMMUNITY. 

microns), is non-motile and shows polar staining. 
It resembles the plague bacillus in form, but is 
somewhat smaller, and does not show the exten- 
sive involution forms of the latter. In the ulcer 
it lies singly, in small groups, or more characteris- 
tically in the form of bands, made up of two or 
more parallel chains, which infiltrate the wall of 
the ulcer. Large numbers are often found in the 
polymorphonuclear leucocytes of the pus, par- 
ticularly at an early stage of the lesion (Kraeft- 
ing). Great difficulty was encountered in culti- 
vating the bacillus, and Ducreyi first success was 
obtained with a medium which contained human 
skin. It has since been cultivated on agar which 
contains the blood or serum of man, rabbit or 
dog. Himmel attempted to cultivate it in the 
fresh deflbrinated blood of the guinea-pig, but 
was unsuccessful because the bacilli were phago- 
cytized by the leucocytes (Babes). 

An ulcer resembling that of soft chancre may 
be produced in the ape, and also in the cat, by the 
inoculation of pure cultures. Didey reinoculated 
man, successfully, from the ulcers of the cat. 
When living cultures are injected into the guinea- 
pig (peritoneal cavity, subcutaneous tissue, dura 
mater), the bacilli are quickly taken up by leuco- 
cytes and digested (Himmel). Himmel reports 
having so decreased the resistance of guinea-pigs 
by peritoneal injections of lactic acid that they 
became susceptible to infection. After two or 
three passages the culture became so virulent that 
fatal bacteriemia was caused without previously 
lowering the resistance of the animals. 



FRIEDLAXDER'S BACILLUS. 571 

In man the infection is transmitted to the in- 
guinal lymph glands, but never becomes general. 

One attack in man does not confer lasting im- 
munity. Spontaneous recovery occurs, but its 
cause is not known. Inasmuch as the bacilli are 
found within leucocytes, phagocytosis may be a 
factor in recovery. The readiness with which the 
autoinoculation of adjacent skin takes place, even 
after the disease has existed for some time, sug- 
gests that general immunity is not established. 

IX. BACILLUS OF FRIEDLANDER AND OTHER MEM- 
BERS OE THE CAPSULE-FORMING GROUP. 

The bacillus of Friedlander, or Bacillus pneu- capsuiated 
mortice, is the type of a rather large group of bac- 
teria, called the Friedlander group, or the group 
of Bacillus mucosus capsulatus. In addition to 
the ability to produce a mucus-like capsule or en- 
velop, they have in general the following charac- 
teristics (Abel) : short, plump rods, varying in 
their proportions, having no motion, no flagella, 
no spore formation, and not staining by Gram's 
method. They form mucus-like masses in cul- 
tures, do not liquefy gelatin and are facultative 
anaerobes. They are widely distributed in nature, 
vary from innocuousness to extreme pathogenicity 
for animals, are rarely found in the mouth, nose 
and bronchi normally (bacillus of Friedlander), 
one type being a normal inhabitant of the intes- 
tines, especially in children (B. laciis aerogenes). 
Perkins has been able to classify the members of 
this group on the basis of their fermenting powers 
for lactose and saccharose. He found their viru- 
lence for animals, immunization and agglutination 
tests, too variable to serve as bases for classifies- 



572 



INFECTION AND IMMUNITY. 



Pneumonia 

Caused by 

Friedlancler's 

Bacillus. 



Rhinoscle- 

roina and 

Ozena. 



tion. In man three members of the group — they 
may be the same organism or variations of a type 
— are of interest from the standpoint of infection : 
Bacillus of Friedlander, the bacillus of rhinoscle- 
roma and the ozena bacillus. 

In 129 cases of acute inflammation of the lungs, 
Weichselbaum found the bacillus of pneumonia 
nine times, twice with streptococci and once with 
the diplococcus of pneumonia. The organism 
causes lobular pneumonia more frequently than 
lobar. The homogeneous non-granular surface, 
and the large amount of fluid of a viscid or mu- 
cous consistence, are characteristic anatomic feat- 
ures. The alveoli contain massive numbers of the 
bacilli. The bacillus of Friedlander is found also 
as the cause of pyelitis, cystitis, pyelonephritis, 
serous or purulent pericarditis, pleuritis and 
meningitis, which may be accompanied by brain 
abscesses. Meningitis when produced by this or- 
ganism usually or always is secondary to infection 
in other parts of the body by the same organism 
(middle ear and accessory sinuses of the nose). 

An organism of the Friedlander type is found 
with few exceptions in the tissues in rhinoscle- 
roma, and by many is considered as the cause of 
the condition. A similar organism is found con- 
stantly in the secretions and crusts in ozena. 

Antiserums of distinct power have not been ob- 
tained for members of the group. Prolonged im- 
munization with some strains yields an agglutinat- 
ing serum of low value. The agglutination re- 
action is of no value for identification of the dif- 
ferent members of the group, nor for clinical 
diagnosis. 



CHAPTER XXVII. 
GROUP IV. 



Infectious diseases which usually are chronic, 
but may run acute courses. They are characterized 
by marked local tissue changes, which exert a lim- 
iting influence on the processes, and include the 
infectious granulomata, excepting syphilis. Infec- 
tion produces little or no immunity. In some in- 
stances the prolonged immunization of animals in- 
duces increased resistance to infection (tuberculo- 
sis) ; in other instances this has not been deter- 
mined, or is difficult of determination because of 
the non-susceptibility of the animals used to 
the corresponding infections. The serums of im- 
munized animals, in so far as this subject has been 
investigated, show little or no protective or cura- 
tive power. 

I. TUBERCULOSIS. 

Klemke, in 1843, but more particularly Ville- 
min, in 1865, demonstrated the infectiousness of 
tuberculosis by animal experiments, and these re- 
sults were substantiated later by such investigators 
as Klebs, Chauveau, Baumgarten and Cohnheim. 
Baumgarten first saw the tubercle bacillus in sec- 
tions of tuberculous material from which the tis- 
sue cells had been dissolved by potassium hydroxid, 
and at almost the same time Koch succeeded in 
demonstrating its presence in all tuberculous 
lesions by a special staining method. He eventu- 
ally obtained the organism in pure cultures with 



tics of tlie 



574 INFECTION AND IMMUNITY. 

which he again produced tuberculosis in experi- 
ment animals. 
ciiaracteris- The tubercle bacillus is an obligate aerobic para- 
site, has the form of a slender, non-flagellated rod, 
often slightly curved, from 2 to 4 microns long 
and from 0.3 to 0.5 microns broad. In stained and 
even in unstained specimens, when properly 
treated, a number of spherical, oval or elongated 
clear spaces can be seen which Koch at one time 
thought to be spores. They are now considered 
either as vacuoles, or as representing some form of 
degeneration or reserve nutritious material. Spore 
formation is uncertain. The organism is sup- 
posed to possess a membrane which may be re- 
sponsible for its strong resistance against heat and 
desiccation. Feinberg speaks of a nucleus (?) which 
may be demonstrated by a modified Eomanowsky 
stain. The organism shows many variations in its 
morphology under different conditions. It often 
exists in isolated clumps, either in cultures or in 
tissues, and may be excreted as such in the urine. 
In certain cultures and sometimes in animal tis- 
sues it grows in the form of longer or shorter 
branching threads, in this respect resembling acti- 
nomyces. This last occurrence has led a number 
of authorities to class the tubercle bacillus as a 
streptothrix, while others would give it an inter- 
mediate position between true bacteria (schizomy- 
cetes) and the streptothrix (a hyphomyces). Oval 
or spherical degeneration forms, the capsules or 
corpuscles of Schron, are found in advanced tuber- 
culosis of the lymph glands and other organs in 
which there is a great deal of necrosis. 

The tubercle bacillus is one of a group of organ- 
isms which are said to be "acid fast" in their 



TUBERCLE BACILLUS. 575 

staining properties. When stained with the carbol staining 
fuchsin of Ziehl and subjected to the action of ropei 
mineral acids in dilute solutions the fuchsin is not 
removed. After counterstaining with methylene 
blue, the tubercle bacilli appear red, whereas other 
organisms, not "acid fast," are stained with the 
methylene blue. It is not difficult to recognize the 
bacilli in sections of tissue when the proper technic 
is used, although the search is at times a laborious 
one. In old processes the organism often can not 
be recognized, and recourse to animal inoculation 
may be necessary in order to demonstrate the ex- 
istence of tuberculosis. 

Much has demonstrated in such cases, however, 
the presence of granular forms of tubercle bacilli 
which are not acid fast but which stain by a modi- 
fication of Gram's method. 

Ordinarily it is a difficult task to obtain the Cultivation. 
tubercle bacillus in pure culture, and the technic 
we need not consider here. Even under the best 
conditions growth is very slow, and may not be 
recognizable to the naked eye for from six to ten 
days. Coagulated bovine serum to which has 
been added from 2 to 4 per cent, glycerin is the 
most favorable culture medium. Good growth oc- 
curs also in glycerin agar, in glycerin bouillon 
and on potatoes. The optimum temperature is 37° 
C. ; growth does not occur above 42° C. nor below 
30° C. When a small amount of culture is planted 
on the surface of glycerin bouillon it proliferates 
slowly to form a heavy membrane. In time this 
growth sinks from its own weight and a new mem- 
brane forms. This process continues until large 
masses have accumulated at the bottom of the 
flask. 



576 



INFECTION AND IMMUNITY. 



Resistance. In its resistance to desiccation the tubercle ba- 
cillus is exceeded only by spore-forming organisms ; 
it lives approximately for three months in dried 
sputum which appears to form a protective coat- 
ing about it. Direct sunlight destroys it in a few 
hours at the most, whereas diffuse light kills it 
only after from five to seven days (Koch). Tt is 
said that the guinea-pig when exposed to sunlight 
withstands tuberculosis for a longer time than one 
which is kept in the dark. Roentgen rays are bac- 
tericidal for the organism, killing it in about one 
hour (Eieder). Under moist heat a temperature 
of 55° C. kills it in from four to six hours, 60° C. 
in one hour, 70° C. in from ten to twenty minutes, 
80° C. in five minutes, from 90° to 95° C. in from 
one to two minutes. When embedded in sputum 
it is more resistant, five minutes being required to 
kill it at the boiling temperature. Corrosive sub- 
limate is not a good disinfectant in this case, inas- 
much as it produces an albuminous precipitate 
around the organism which prevents penetration 
of the sublimate. Five per cent, carbolic acid 
added to equal parts of sputum kills the bacil- 
lus in 24 hours. Formalin vapor is a good dis- 
infectant for dry, but not for moist sputum. Iodo- 
• form is not a good disinfectant, in spite of its bene- 
ficial influence on the infectious process. The re- 
sistance of the bacillus to gastric digestion has an 
important bearing on the occurrence of infection 
in the intestinal tract. The gastric juice of the 
dog, in one instance, failed to kill the bacillus after 
six hours' exposure, although it had the power of 
prohibiting proliferation. 
virulence. The bacillus of human tuberculosis, although 
fairly constant in its virulence, may be attenuated 



TUBERCLE BACILLUS. 577 

by various means. Its prolonged existence in putrid 
sputum decreases its virulence and a similar de- 
crease occurs on potato, in old cultures or in those 
which contain iodoform, boracic acid and some 
other substances. Inoculation with such cultures 
produces a chronic form of tuberculosis in animals 
which may heal. In other instances cultures which 
have grown on artificial media for many years re- 
tained their original virulence. 

The organism contains about 90 per cent, of 
water. One-fourth of a dried bacterial mass may 
be extracted as a wax-like or fat-like substance by 
a mixture of alcohol and ether. The acid-fast 
staining property of the bacillus depends on this 
substance. The remaining portion of the mass, 
consisting largely of proteins, which may be ex- 
tracted by dilute alkalies, contains a toxic nucleo- 
albumin. Cellulose, representing a portion of the 
capsular substance, is also found in the residue. 

Killed cultures when given subcutaneously pro- Toxic 
duce necrosis, abscesses, caseation, marasmus, and 
a subnormal temperature. When given to rabbits 
and guinea-pigs intravenously they cause rapid 
emaciation and death in from a few days to a few 
weeks. By beginning with very minute doses, how- 
ever, the animals may be gradually habituated to 
intoxication by the dead bacilli and eventually 
withstand large doses. The same holds true of the 
various toxic substances, including tuberculin, 
which may be extracted from cultures. The pro- 
teins and alkaline extracts cause abscesses when 
given subcutaneously. The fever-producing sub- 
stance which is present in the preparations men- 
tioned below is one of the metabolic products of 
the bacillus, rather than a constituent of the bac- 



Products. 



578 INFECTION AND IMMUNITY. 

serial cell (Koch). This substance is 100 times 
as toxic for tuberculous animals as for healthy and 
causes an increase in the eosinophiles of the blood. 
In addition to the fever-producing substance, 
Maragliano and others recognize as a constituent 
of the bacillus a heat susceptible "toxalbumin" 
(destroyed at 100° C.) which reduces temperature. 
Hammerschlag speaks of a toxin which in animals 
causes fatal convulsions. The toxic products of the 
tubercle bacillus show their greatest toxicity when 
injected into the brain, and this method of injec- 
tion has been suggested for the standardization of 
tuberculin. 
Tuberculin. Of the toxic preparations of the bacillus the 
greatest interest attaches to tuberculin which 
Koch, in 1891, announced as an agent which could 
be used for the specific diagnosis of tuberculosis 
and which, when properly administered, had cer- 
tain curative effects. Its preparation is simple. 
Cultures are allowed to grow for four weeks in 
peptone bouillon which contains 5 per cent, of 
glycerin. At the end of this time the organisms 
are killed by exposure to a temperature of 100° C. 
for one hour (Marx). The fluid is reduced to one- 
tenth its original volume by evaporation under a 
vacuum at a low temperature and the bacterial 
cells are eventually removed by filtration. The 
percentage of glycerin which is present in the final 
preparation acts as a preservative, but 0.5 per 
cent, carbolic acid may be added in addition. The 
active substance in tuberculin may be precipitated 
by 66 per cent, alcohol; its chemical nature re- 
mains unknown. 

In addition to the "old tuberculin," which has 
just been described, Koch has made several other 



. 



TUBERCULIN. 579 

preparations having similar properties, the use of "ta,» «tr' 
which has been proposed for diagnostic and cura- an 
tive purposes and for convenience in carrying out 
the agglutination reaction. One of these, "TA," 
is an alkaline preparation which is made by ex- 
tracting cultures with 1/10 normal sodium hy- 
droxid solution. Its diagnostic value was equal 
to or exceeded that of tuberculin because of 
the longer duration of the reaction. However, in 
view of the fact that it contained undissolved 
cells, which caused the formation of abscesses at 
the point of injection, its use was not encouraged. 
For purposes of immunization Koch prepared a 
fluid which contained all the bacterial constituents 
and which at the same time is readily absorbed 
without abscess formation. For its preparation 
dried masses of the organism are ground up in an 
agate mortar; after suspension in distilled water 
and centrifugation, the emulsion consists of two 
layers. The overlying opalescent whitish fluid was 
designated as "TO" (Tuberculin-Obers). After 
removal of the fluid from the precipitate the lat- 
ter was again dried and ground, suspended in 
water and centrifugated as before, and the process 
repeated until none of the sediment remained. The 
different fractions of fluid, except the "TO," were 
combined to constitute "TK" (Tuberculin-Rest) , 
which is really an emulsion of minute fragments 
of cells. It is readily absorbed and does not cause 
the formation of abscesses. This is commonly 
called Koch's "new tuberculin." Still another 
preparation which Koch later devised for active 
immunization and for convenience in performing 
the agglutination test consists of dried and ground 
up bacilli which are suspended in equal parts of 






Tuberculins. 



580 INFECTION AND IMMUNITY. 

glycerin and water, Neutuberculin Koch (Bazillen- 
emulsion) . 
other Preparations which in many respects are analo- 
gous to those of Koch have been made by various 
investigators; the tuberculocidin of Klebs, the tu- 
berculins of de Schweinitz and Dorset and that of 
Denys, the two tubercule toxins of Maragliano, 
which he utilizes for the preparation of antitoxic 
serums, the oxytuberculin of Herschfelder, the 
"TD" and the "TDK" of Behring and the tubercu- 
loplasmin of Buchner. Marmorek claims to have 
obtained the true toxin of the tubercle bacillus by 
growing young, vigorous cultures on a complicated 
medium, denying that tuberculin represents the 
true toxin of the organism. 
standard- Tuberculin can not be standardized with accur- 
ization. ac y^ Because of the extraordinary susceptibility of 
tuberculous animals to tuberculin, Koch decided to 
estimate its value by the quantity required to kill 
such animals. From 0.5 to 1 c.c. of tuberculin, 
when injected into a healthy guinea-pig, causes 
neither a local nor a general reaction, whereas 
from 0.1 to 0.15 c.c. kills a tuberculous guinea- 
pig in from 24 to 48 hours. For stand- 
ardization von Lingelsheim recommends intracere- 
bral injection into healthy guinea-pigs, because 
of the extreme toxicity of tuberculin when 
introduced into the central nervous system; only 
1/180 as much tuberculin was required to cause 
death by intracerebral injections as compared with 
subcutaneous or intraperitoneal. Behring bases the 
value of tuberculin on its toxicity for healthy 
guinea-pigs and in his terms the expression "1 
c.cm. = 1,000 M." means that one gram of the 
toxin is fatal to 1,000 grams of guinea-pig tissue. 



TUBERCULIN. 581 

His "TD" has a value of 1,250 M., and "TDK," 

12,500 M. For the standardization of old tuber- 
culin, the following method is used in the Eoyal 
Institute for Experimental Therapy, at Frankfort, 
Germany: Two series of guinea-pigs infected 
with a pure culture of tubercle bacilli are injected 
with decreasing doses of tuberculin. In one series 
a standard preparation of tuberculin is used; in 
the second series, the tuberculin to be tested is 
utilized. If the minimum fatal dose of the sample 
to be tested is the same as the standard, it is of 
official strength. If stronger than the standard it 
is diluted to the desired strength. If weaker it is 
concentrated by further evaporation. 

The tubercle bacillus undergoes no proliferation 
outside the body and its occurrence in nature de- 
pends on the distribution of the infected excre- 
tions, particularly the sputum, of man. Hence it 
is found most abundantly in the rooms and homes 
of patients and in tuberculous wards of hospitals. 
Eeception of sputum on the handkerchief of the 
patient, where it subsequently dries, and its dis- 
charge on the floor in public places, where it quick- 
ly becomes pulverized, as in street cars, are condi- 
tions which favor dissemination and the infection 
of others. In unconfined places which are exposed 
to the action of light and sun, as the streets and 
sidewalks, the danger is less on account of the 
shorter life of the organism under these conditions 
and the greater volume of surrounding air. The 
calculation of Heller that a tuberculous patient 
may excrete 7,200,000,000 of bacilli in a day sug- 
gests the number which may lurk in a single mis- 
placed portion of sputum. Sputum which is kept 



Dissemi- 
nation, 



Dried 
Sputum. 



582 INFECTION AND IMMUNITY. 

moist is not a source of particular danger, inas- 
much as ordinary currents of air do not dissipate 
it in the form of infected drops. Droplets of spu- 
tum which are expelled by coughing contribute 
greatly to the infected dust which surrounds a 
patient. 

Large quantities of bacilli are often excreted in 
the feces in intestinal tuberculosis and in the urine 
in genitourinary tuberculosis, or in general miliary 
tuberculosis with localization of the process in the 
urinary organs. The pus from tuberculous ab- 
scesses commonly is infectious. 
Bovine and Great interest attaches to the possibility of infec- 
bercuiosis. tion of man by the milk and meat of tuberculous 
cattle. Previous to 1901, through the work of 
Smith and others, the opinion had been gaining 
ground that the bacilli of human and bovine tuber- 
culosis are not identical. It was not always possi- 
ble to produce tuberculosis in cattle by feeding 
them or causing them to inhale tuberculous spu- 
tum or pure cultures which were highly infectious 
for other experiment animals, although bacilli of 
bovine origin invariably caused the disease in cattle 
when administered in a similar manner. It seemed 
then that the two bacilli are not identical in their 
pathogenic powers. Koch having performed such 
experiments without being able to infect cattle with 
bacilli of human origin expressed his belief that 
the converse also is true, i. e.,that the bovine ba- 
cillus is not pathogenic for man. Perhaps the 
strongest argument in favor of this view is the 
circumstance that primary tuberculosis of the in- 
testines and mesenteric glands is very rare in chil- 
dren, who drink a good deal of milk, in spite of 
the great prevalence of tuberculous cows. Manv 



TYPES OF TUBERCLE. 583 

protests followed the announcement of Koch's 
views, and in a short time a number of investiga- 
tors showed, first, that it is possible in some cases 
to produce tuberculosis in cattle with tuberculous 
material from man, and, second, tha.t infection of 
man with the bovine bacillus is possible. Un- 
questionable proof of the latter consists in the de- 
velopment of localized tuberculosis in those who 
have performed autopsies on tuberculous cattle 
(Eavenel and others). In an examination of 43.6 
cases of human tuberculosis, Park and Krumwiede 
found bacilli of the bovine type in fifty-two cases 
(11.9 per cent.). In persons over 16 years of age, 
constituting 297 of the 436 cases, one case of 
tuberculosis with bacilli of the bovine type was 
found (0.39 per cent.). In children between the 
ages of 5 and 16, nine out of fifty-four cases were 
due to the bovine type of bacilli (18.5 per cent.). 
In eighty-nine cases in which the patients were 
under 5 years of age, twenty-two due to the bovine 
type were found (nearly one-fourth). The cases 
showing bovine types of bacilli were mostly infec- 
tions of the abdomen and glands of the neck. In 
no case of primary pulmonary infection were 
bacilli of the bovine type found. 

The following points serve to distinguish the 
bovine bacillus from the human : First, the bovine Bacilli. 
bacillus is shorter than the human; second, when 
first cultivated it grows feebly in media in which 
the human bacillus flourishes; third, it has a 
higher virulence for rabbits and guinea-pigs, and, 
fourth, it produces more extensive lesions in cattle. 
To these Smith has added a fifth point, which he 
has found to be distinctive in a large number of 



Differences 
in the 



584 INFECTION AND IMMUNITY. 

cultures: In bouillon which contains 5 per cent, 
of glycerin and which is 2 per cent, acid to phenol- 
phthalein the bovine bacillus produces a neutral 
or faintly alkaline reaction in from three to sev- 
eral weeks, whereas the human bacillus, after caus- 
ing temporary alkalinity, produces a terminal 
acidity of from 0.5 to 1.5 per cent. On the basis 
of this test and other points the bacilli of two cases 
of mesenteric tuberculosis in man were recognized 
as bovine in type. In view of the fact that infec- 
tion of man with the bovine bacillus has been 
shown to be possible, we are justified in con- 
sidering the meat and especially the milk of tuber- 
culous cattle as the probable sources of infection 
in a limited number of cases. 
congenital Comparatively few cases of undoubted congeni- 

nherenlosis. . , , , r . ■, -, ■, t i • i 

tal tuberculosis have been observed, and in sucn 
cases the mothers are usually in an advanced stage 
of the disease. It is probable that the organisms 
reach the fetus following metastatic invasion of the 
placenta. In a number of cases in which the 
mother had advanced tuberculosis the organs and 
blood of the fetus (stillborn or dying soon after 
birth), contained very many bacilli, although his- 
tologic lesions had not as yet been produced 
Warthin and Cowie suggest that the tissues of tiu 
fetus may possess considerable immunity in such 
cases. Baumgarten is a strong believer in the pos- 
sibility that tubercle bacilli may pass to the fetus 
during pregnancy and, remaining latent in some 
of the tissues (lymph glands) for a long period, 
cause active tuberculosis later in life. Others who 
are less radical still admit that we should consider 
this as a possibility (Warthin and Cowie, Har- 



INFECTION ATRIA. 585 

bitz). The possibility of transmission of tubercu- 
losis by means of tubercle bacilli in the spermatic 
fluid should also be considered. Although no 
proof of such infection exists, the presence of 
bacilli in the spermatic fluid has been demonstra- 
ted, particularly in men with tuberculous epididy- 
mitis. 

Pulmonary tuberculosis is by far the most com- infection 
mon form of the disease in man, and without doubt 
this usually is due to inhalation of the dried and 
pulverized sputum of tuberculous patients. Drop 
infection may well occur in the case of those who 
are in intimate contact with the sick. In kissing, 
direct infection from mouth to mouth is a danger- 
ous possibility. 

The reason for the inception of pulmonary tu- 
berculosis in the apex in so many cases is not clear- 
ly recognized, although it is often referred to the 
relative immobility of this tissue, which renders 
excretion more difficult and affords improper 
aeration. These conditions not only allow -the or- 
ganisms to accumulate and to proliferate, but the 
insufficient oxygenation probably causes a low tis- 
sue resistance. The suggestion which has been 
made that apical tuberculosis is the result of ex- 
tension of the disease from the cervical glands does 
not correspond with the condition seen in tubercu- 
losis of adults in whom the cervical adenitis is 
commonly wanting. 

The "anatomic tubercle" is a primary infection 
of the skin; lupus vulgaris, it is supposed, may be 
either a primary infection or secondary to tubercu- 
losis in some other organ; ulcerative tuberculosis 
is usually a secondary lesion, often occurring by 
direct extension from tuberculous lymph glands. 



586 INFECTION AND IMMUNITY. 

Tuberculosis of the nose is uncommon. Infection 
of the tonsils is not infrequent and probably is a 
common cause of secondary tuberculosis of the cer- 
vical lymph glands. Primary infection of the 
pharynx sometimes occurs and large, coarse granu- 
lations of this surface have been proved in some 
cases to be of a tuberculous nature. Tuberculosis 
of the pharynx and larynx, however, most often 
arises from infection with tuberculous sputum. 

In the process of dust infection of the lungs, and 
also by other means, many organisms lodge on the 
mucous membranes of the nose, mouth, pharynx, 
trachea and larger bronchi, but usually without 
producing a tuberculous infection. On account of 
the movement of the ciliated epithelium, tortuos- 
ity of the nasal channels, excretion of the bacilli 
with mucus, the conditions at these points are not 
favorable for infection. 

Tuberculous ulcers of the esophagus and stom- 
ach are very rare, as is primary tuberculosis of the 
intestines. Secondary tuberculosis of the intes- 
tines usually is caused by the infected sputum 
which the patient swallows. Primary infection of 
the genital organs may arise from direct contact. 

That tubercle bacilli have often been found on 
the hands and finger nails of the sick as well as on 
those who are intimately associated with them is a 
significant fact in relation to the possibility of in- 
fection by direct contact. 
Metastases. From a given focus tubercle bacilli extend to 
other structures in several ways. On more or less 
theoretical grounds one speaks of "extension by 
growth" of the organism into contiguous tissues. 
The commonest method of extension, however, is 



METASTASIS IX TUBERCULOSIS. 587 

that of metastasis by way of the lymph channels. 
When bacilli penetrate a surface, with or without 
the formation of a lesion at the point of entrance, 
as in the month cavity, intestinal canal, or bron- 
chial surface, they are carried to the lymph glands 
of the region in which the tuberculous process is 
instituted. As in plague, the infection atrium at 
times is indicated by the set of glands which is in- 
volved. In certain localities the secondary invasion 
of other structures takes place directly without the 
intermediate involvement of lymph glands, as in 
tuberculous meningitis caused by extension from 
the middle ear, and tuberculous peritonitis or peri- 
carditis by extension from the pleura. Very fre- 
quently tuberculosis of the lymph glands and other 
tissues heals spontaneously, as described below. 
In case healing does not occur, metastases con- 
tinue from one lymph gland to another and to new 
sets of glands until the larger lymph channels are 
reached, as a consequence of which extensive re- 
localization of a focus often causes a wide depart- 
gional or general tuberculosis results. Accidental 
localization of a focus often causes a wide depart- 
ure from the slow development just described. Not 
infrequently tuberculosis in a lymph gland, which 
is contiguous to a large lymph channel, as the tho- 
racic duct, invades the wall of the latter, the sur- 
face softens from caseation or liquefaction and the 
contents, impregnated with countless bacilli, are 
gradually thrown into the circulation. Miliary 
tuberculosis, first of the lungs and then of other 
tissues, through the arterial circulation, follows 
such an accident. A similar course with variations 
in localization, follows invasion of the walls of 
branches of the pulmonary artery or vein. Kup- 
ture of a focus into a bronchus is followed by re- 



588 INFECTION AND IMMUNITY. 

gional or more extensive dissemination of the ba- 
cilli throughout the lungs by respiratory forces. 
A slower eccentric extension is seen, particularly 
in the lungs, in which smaller and larger areas of 
consolidation occur. By means of short lymphatic 
metastases into contiguous territory new foci are 
instituted, which eventually fuse with the original 
lesion. It is suggested and generally believed that 
bacilli may be carried longer or shorter distances 
by wandering phagocytic cells. When tuberculosis 
once involves a surface like that of the pleura, peri- 
toneum, pericardium or pelvis of the kidney, the 
whole surface frequently becomes involved in 
thickly studded miliary tubercles. It is probable 
that a great deal of dissemination is accomplished 
by the movements of the fluids and the surfaces of 
these cavities. In other instances, as in the ure- 
ters, Fallopian tubes and spermatic cords, exten- 
sion seems to occur in the submucous tissue by 
means of the lymphatics. The autopsy often dis- 
closes that tuberculosis which appeared to be "pri- 
mary" in such organs as bones, suprarenal glands, 
and meninges was preceded by an old process in a 
lymph gland from which metastases occurred to the 
tissues in question. 
The Tubercle Certain anatomic conditions produced in tuber- 
Tissue culosis which are associated with recovery from the 
disease, or the contrary, may be referred to. The 
tubercle, the histologic unit of the tuberculous 
process, is produced as follows, according to the 
interpretations of Baumgarten: When a bacillus 
reaches a lymph gland, for example, it multiplies 
slowly and, partly through its presence as a foreign 
body, but particularly through its toxic secretions, 
injures the surrounding connective tissue and en- 



Clianges. 



THE TUBERCLE. 589 

dothelial cells to a certain degree. Under some 
circumstances, especially in the parenchymatous 
organs and lymph glands, this injury may be so 
great as to cause the death of the adjacent cells 
(focal necrosis). When it is of a lower order the 
connective tissue and endothelial cells respond to 
the stimulus by dividing mitotically and eventu- 
ally accumulate in large numbers within a limited 
area surrounding the micro-organisms. Not only 
the endothelial cells of the lymph spaces, but also 
those of the adjacent blood vessels, take part in 
the proliferation, many of the vessels being obliter- 
ated in consequence. Not infrequently bacilli aro 
ingested by the new cells, although the ability of 
the latter to destroy the organisms is not clearly 
established. Metchnikoff says that tubercle bacilli 
may remain intracellular for many months and, 
although not killed, the pathogenicity is decreased 
or destroyed. The new cells are of polygonal shape, 
are fairly rich in cytoplasm, contain large vesicular 
nuclei and are termed "epithelioid" cells. 

Certain of the epithelioid cells, usually those in g**" 1 * Cells 
the center of the tubercle, where the bacilli are 
most numerous, undergo atypical proliferation in 
that repeated nuclear division takes place without 
corresponding division of the cytoplasm. This 
process results in the formation of the multinu- 
clear giant cell which is so characteristic of the 
well-developed tubercle, although not distinctive of 
the disease. According to Weigert, the failure of 
complete cell division is due to injury to the cyto- 
plasm (partial necrosis) by the bacteria which the 
cell contains. Metchnikoff and others take a dif- 
ferent view of the formation of giant cells, con- 
sidering that they represent individual epithelioid 



590 INFECTION AND IMMUNITY. 

cells which have fused to form a multinuclear 
mass. 

Retrogres- Still more remote from the center of the tuber- 
cle, that is, surrounding the epithelioid cells, wan- 
dering lymphoid and plasmal cells accumulate. 
Certain retrogressive changes, especially necrosis 
and caseation, characterize the further history of 
the tubercle, although these changes do not occur 
equally early nor with equal intensity in all cases. 
Necrosis begins in the center of the lesion, and the 
view is often expressed that the formation of the 
giant cell is the first indication of the retrogressive 
change. Cell degenerations, however, with karyor- 
rhexis may occur before giant cells have formed. 
With the death of the central tissue there occurs 
sooner or later the death of many of the bacilli in 
this portion of the tubercle. The progressive for- 
mation of new tissue continues in the periphery as 
the degenerative changes take place toward the 
center; the tubercle enlarges, both epithelioid and 
the surrounding lymphoid cells increase corre- 

Formation spondingly, and new giant cells form at the periph- 
Tissrae! ery of the necrotic center, only to be included in 
the degenerated area as the latter extends. In 
favorable cases, in which the virulence of the or- 
ganism is low or the resistance of the individual 
strong, the tuberculous area is eventually sur- 
rounded by adult fibrous tissue which in a sense 
accomplishes the isolation of the infected area. 
Without question such a capsule of scar tissue is an 
obstacle to the extension of the tuberculous proc- 
ess, whether it surrounds a nodule in a lymph 
gland, a cold abscess or a tuberculous sinus. 
Further steps in the healing consist of caseation of 
the entire area, its partial or complete substitution 



MIXED IXFECTJONS. 



591 



by connective tissue (tuberculous scar), or partial 
impregnation with lime salts (calcification). Not 
infrequently the caseous portion of a nodule under- 
goes liquefaction, which some have referred to the 
action of proteolytic ferments. The contents of 
such foci finally become sterile. In the event that 
healing of this nature does not occur, the infection 
is transmitted to other organs as described above. 

The temperature, loss of weight, fever, increased 
cardiac action, and arteriosclerosis which are seen 
in tuberculosis indicate that the products of the 
bacillus have a profound effect on the functions 
of the body, and produce great disturbances in 
metabolism, although they seem to have no marked 
selective action for particular tissues. Many dis- 
turbances are secondary to changes produced in 
particular organs and are not referable to specific 
action of the toxins, such as those which are 
consequent on poor oxygenation in pulmonary 
tuberculosis, and the amyloid degeneration which 
follows prolonged suppurative tuberculosis. 

Mixed infection, especially with the streptococ- 
cus, plays a very important part in the course of 
pulmonary tuberculosis, especially in the caseous 
and cavernous forms. Staphylococci, B. pyocya- 
neus, various diplococci, the pneumococcus, bacil- 
lus of Friedlander, diphtheria and pseudo-diph- 
theria bacilli, and the influenza bacillus are also 
found as secondary organisms in pulmonary tuber- 
culosis. Some of them invade the surrounding 
healthy tissue, cause lobular consolidations, and in 
this way probably prepare a favorable soil for 
further extension of the tuberculous process. They 
doubtless hasten the liquefaction of caseated tissue, 
a step in the formation of abscesses. The high and 



Caseation, 
Calcification 
and Lique- 
faction. 



General and 

"Secondary 

Disturbances. 



Infections. 



592 INFECTION AND IMMUNITY. 

irregular fever often seen in advanced tuberculosis 
is commonly septic in its cause, and a terminal 
streptococcus septicemia is not infrequent. It is 
evident that mixed infections may complicate at- 
tempts at serum therapy. 
principles of The essential principles in the prevention of 
tuberculosis consist of, first, the early recognition 
of the disease, so that the patient may be properly 
treated and cured, if possible, with the result that 
a new center of contagion is avoided; second, the 
rendering of well-developed cases harmless by suit- 
able isolation and proper disposal of infected ex- 
cretions; third, the disinfection of the rooms, 
clothing, linen and surroundings of tuberculous 
patients. A fourth point, the prohibition of mar- 
riage among the tuberculous, is one of great con- 
sequence, although we have little ground to hope 
for its realization. A fifth point, not yet fully 
established, is the possibility of universal vaccina- 
tion against the disease. 
Disposal The collection of infected sputum in properly 

of Sputum. r r r J 

constructed water-proof paper boxes, which, with 
their contents, should be burned daily, is the safest 
method of disposing of this material, and the most 
effective means of preventing infection of the pa- 
tient's surroundings. Metallic, glass or earthen- 
ware sputum-cups containing 5 per cent, phenol 
solution are serviceable, but must be subjected to 
frequent cleansing. When sputum is collected on 
a handkerchief the latter should be boiled within 
twelve hours and not allowed to dry ; that the hands 
of the patient are likely to be contaminated from 
the handkerchief is evident. In coughing, the 
handkerchief should be held to the mouth to catch 



Disinfection. 



PROPHYLAXIS. 593 

droplets of sputum and saliva which are expelled. 
The ordinances and rules which prohibit expecto- 
ration in street cars and other public places should 
be enforced. When bacilli are discharged in the 
urine and feces or in the pus of tuberculous ab- 
scesses and sinuses, these secretions should be dis- 
infected by suitable means (chlorid of lime). 
Healthy persons should come in contact with the 
tuberculous as little as possible, and the eating 
utensils of the latter should be used by no one else. 

The floor of a room which is inhabited by a tuber- 
culous person should always be moistened before it 
is swept, in order to avoid stirring up the dust. 
After the death or removal of a patient, the entire 
surface of the room and all its contents should be 
thoroughly disinfected by appropriate means. The 
proper disinfection of the premises which were 
once occupied by a consumptive should be a legal 
requirement, just as similar procedures are de- 
manded in the case of smallpox and some other 
contagious diseases. 

The special hospital in which the indigent tuber- 
culous may be properly cared for and isolated has 
been a powerful factor in causing the decrease of 
tuberculosis which has been noted in many coun- 
tries. The removal of a patient to such an institu- 
tion means the elimination of an infected focus 
from the community. 

Cold-blooded animals (fish, amphibians, rep- ^ U | S -^ ept n " d 
tiles), and most birds are not highly susceptible to immnnity. 
tuberculosis, although special varieties of the ba- 
cillus cause the disease in certain of them under 
natural conditions. When tubercle bacilli are in- 
jected into the circulation of birds, they may re- 
main in the blood and organs for months, produc- 



Racial and 
Individual 



594 INFECTION AND IMMUNITY. 

ing little or no tissue change, although they retain 
their virulence for other animals (guinea-pigs). 
No animal exceeds the guinea-pig in its susceptibil- 
ity to this disease. Goats and sheep are fairly re- 
sistant, and the same is probably true of the horse, 
although its artificial infection is not difficult. 
That different varieties of a species may vary in 
their susceptibility is illustrated by the field mouse, 
which is highly susceptible, and the white mouse, 
variations, which is relatively immune. Although similar 
variations may exist among different races of men, 
they are not readily demonstrated. The high sus- 
ceptibility which appears to exist among certain 
races, as the negro, may be explained in part by un- 
hygienic methods of living, in which safeguards 
against infection are not taken. 

The discovery of healed or healing tuberculous 
foci in 70 to 90 per cent, of all autopsies, in con- 
trast to the 15 to 20 per cent, of deaths from tuber- 
culosis, shows that susceptibility and immunity are 
subject to marked individual variations. The 
ability of an individual to overcome a tuberculous 
infection is referred in a vague way to an unusual 
resistance on his part; his defensive powers are 
said to be strong. Although we remain to a large 
extent in the dark concerning these defensive 
powers, they seem to rest chiefly in the ability of 
the tissues to destroy the bacilli; that is, the re- 
sistance is antibacterial. Many bacilli may be de- 
stroyed by leucocytes or endothelial cells before 
they are able to cause tissue changes. It was stated 
previously that healing in many instances depends 
on isolation of the focus by epithelioid, lymphoid 
and plasma cells, and by connective tissue. On 
general grounds we may assume that a tissue reac- 



Influences. 



IMMUNITY. 595 

tion of this nature takes place with greater vigor 
and rapidity in a strong, healthy person than in 
one of lower vitality. Aside from the question of 
individual resistance, recovery or progressive infec- 
tion may depend on the smaller or larger amount 
of bacilli which gained entrance to the body, as 
well as on their virulence. Experiments show that 
susceptible animals recover from minute doses, 
whereas they succumb to somewhat larger doses of 
bacilli. 

Various external influences increase susceptibil- Predisposing 
ity and resistance. Tuberculosis is to no small de- 
gree a disease of the poor, who so frequently live 
in an undernourished condition, in crowded, dirty 
rooms, with little sunlight and fresh air. The 
disease is more common in the city than in the 
country, where an outdoor life is the rule. Alco- 
holism, diabetes, measles, scarlatina, whooping- 
cough often, and influenza not infrequently, are 
precursors of tuberculosis. Conditions which favor 
anemia, as pulmonary stenosis (rare), predispose 
to pulmonary tuberculosis, whereas insufficiency of 
the left heart, accompanied by congestion of the 
lungs, is not often associated with the disease, al- 
though it has no influence in preventing infection 
in other organs. Tuberculosis is more frequent 
during the first two or three years of life, when 
children are so commonly confined, than from the 
third to the fifteenth year, when they live in the 
open air so largely. From the fifteenth year to 
middle life or later the disease increases in fre- 
quency because of greater exposure to infection. 
Physicians who are familiar with tuberculosis in 
Scandinavian countries and in America comment 






596 INFECTION AND IMMUNITY. 

on the extent to which tuberculosis develops among 
Scandinavians after they come to this country. 
"Hereditary Nothing is commoner than the occurrence of 
several successive cases of phthisis in the members 
of a family, and the expression, heard on all sides, 
that "tuberculosis is in the family," indicates the 
general belief that a family tendency may be trans- 
mitted from generation to generation. During 
recent years, however, closer analysis of the condi- 
tions has led many to doubt the existence or, at any 
rate, the importance of family tendency or inher- 
ited predisposition, and to refer the frequent oc- 
currence of tuberculosis in a family to the greater 
exposure to infection which is occasioned by close 
contact with a pre-existing case. Cornet, who has 
made a close statistical study of tuberculosis, dis- 
credits entirely the hypothesis of hereditary pre- 
disposition, and Cornet and Meyer refer to the 
"habitus pldJiisicus" which we are disposed to 
look on as an objective evidence of hereditary ten- 
dency, as a result rather than a cause of pulmonary 
tuberculosis. It is fair to say that the development 
of tuberculosis in several members of a family is 
not prima facie evidence of the existence of a 
family predisposition for the disease. Where thero 
are tubercle bacilli there is likely to be tuberculosis, 
and the occurrence of the infection in one fur- 
nishes the prerequisite, that is, bacilli, for the de- 
velopment of the disease in other members of the 
family. It is probable that the verdict of family 
tendency has often been pronounced erroneously. 
At present, however, we may not be justified in 
considering the subject a closed chapter. 

It is the commonly accepted opinion that recov- 
ery from tuberculosis does not confer immunity to 



IMMUNITY. 597 

subsequent attacks. Cornet and Meyer suggest as Acquired 
an explanation of this condition that the local le- 
sion is so strictly isolated that a sufficient amount 
of toxin does not escape into the circulation to 
cause a general reaction, hence the formation of an- 
titoxin or other antibodies is impossible. This ex- 
planation seems inadequate, however, when we re- 
member the strong antitoxic immunity which de- 
velops in tetanus and diphtheria in spite of the lo- 
calization of the bacteria. The results of artificial 
immunization, in which unlimited amounts of 
toxic material or bacilli may be injected without 
the formation of satisfactory antitoxins, seem to 
indicate that the toxic constituents of the tubercle 
bacillus lack the power of causing the formation of 
a strong antitoxin. 

In opposition to the prevailing opinion, certain 
observers find ground for the belief that recovery 
from local tuberculosis of the lymph glands, skin or 
bones, actually does render the patients immune to 
pulmonary consumption (Maragliano and others). 
In early experiments Koch noted that when tuber- 
cle bacilli were injected subcutaneously into 
guinea-pigs which were suffering from general tu- 
berculosis, the subcutaneous inoculation remained 
as a local infection and not infrequently healed 
after sloughing. The general infection would seem 
to have increased local resistance. Although other 
investigators failed to duplicate the observation of 
Koch, this result is said to have suggested to him 
the idea of active immunization as a cure for tu- 
berculosis, a method subsequently practiced by 
treatment with the various tuberculins. 

In the United States, Trudeau and de Schwein- 
itz, and in Europe, Koch, Behring, Maragliano 



598 INFECTION AND IMMUNITY. 

Active im- and Baumgarten, with their followers, have prac- 
ticed assiduously the artificial immunization of 
animals with the tubercle bacillus or various prep- 
arations from the organism, with the hope of pro- 
ducing active immunity to the disease. Williams, 
Webb and Barber have successfully immunized 
animals by the injection of living virulent tubercle 
bacilli into the subcutaneous tissue. In these 
experiments, the immunization was begun with a 
single isolated tubercle bacillus as the first dose. 
The immunity was demonstrated by the fact that 
the animals were able to withstand the injection of 
many times the fatal dose of living tubercle bacilli. 
The indications are that in preparation of tubercle 
bacillus vaccines by heat, etc., the antigenic prop- 
erties of the bacilli are unfavorably modified. Eel- 
atively avirulent strains as those cultivated from 
fish, turtle or fowls, have been utilized for the first 
injections. As immunization progresses one of two 
processes may be followed : either the quantity in- 
jected may be increased gradually, as when killed 
or avirulent bacilli are used, or the immunization 
having been begun with avirulent living cultures 
those of higher virulence may be substituted later. 
In any case immunization is difficult and slow, 
and many animals may be lost from cachexia or 
from tuberculosis which develops from hasty pro- 
gression in dosage. The subcutaneous injection 
of intact cells has the disadvantage that local ab- 
scesses frequently develop, and to avoid this the 
intravenous injection of smaller doses has been 
practiced in some instances. For active immuniza- 
tion the "new tuberculin" of Koch containing all 
the cellular constituents in a finely divided form 
has the advantages that it may be given subcu- 



DIAGNOSIS. 599 

taneously without abscess formation and is ab- 
sorbed with some rapidity. An animal or person 
immunized with TE is immune to all the constitu- 
ents of the bacillus. The condition produced by 
active immunization is one of increased resistance 
rather than of absolute immunity; large doses of 
bacilli may cause infection. The nature of the 
new resistance is not satisfactorily established. 

Inasmuch as tuberculin is used not only for Tuberculin 

,. • i . i j? .• • ln Diagnosis 

diagnosis but also lor curative purposes m man 
(active immunization), and since the principles of 
action are similar in both instances, the use of 
tuberculin may be considered at this point. A 
healthy man is not susceptible to moderate doses, 
but a tuberculous man is even more susceptible 
to the toxin than the tuberculous guinea-pig, 
since 1 mg. often causes an intense reaction. 
Weigert classifies the disturbance which tuber- 
culin may produce in the tuberculous as thermal, 
circulatory, respiratory, digestive, nervous and 
vasomotor, and secretory. Necrosis may be pro- 
duced at the point of injection. In so far as the di- 
agnostic use of tuberculin is concerned, we are in- 
terested chiefly in the thermal disturbances, 
which are accompanied by chills, malaise and 
muscular pains. Following injection of a suitable 
quantity, a period of incubation of from eight to 
fourteen hours follows, and at the end of this time 
the temperature rises progressively for two or 
more hours and may reach a maximum of from 40° 
to 41° C. ; after remaining at this point for from 
two to six hours, it recedes rapidly. In addition 
to this general reaction, the toxin causes conges- 
tion, redness and swelling at tne site of the tuber- 
culous lesions, i. e., the foci become surrounded by 



600 INFECTION AND IMMUNITY. 

an inflammatory reaction. This is seen most 
readily in the tubercles of lupus vulgaris, and in 
the lungs declares itself by an increase in rales 
and expectoration, caused by the exudation ac- 
companying the inflammatory reaction. 

For diagnostic purposes the technic of adminis- 
tration is as follows: It must first be assured 
that the patient has no continued fever by noting 
the temperature every two hours for several days. 
One milligram of tuberculin is injected subcu- 
taneously, this amount being obtained by suitable 
dilution of the original solution. It is often advis- 
able in weak or young subjects to use 0.05 or 0.1 
mg. Many authorities never exceed 0.1 mg. as an 
initial dose. If no rise in temperature is produced 
by this amount, a second injection of a larger 
quantity may be given after an interval of two or 
three days. Koch used as high as 10 mg. before 
concluding that the reaction is negative. Lowen- 
stein and others recommend the cumulative action 
of three or four small doses of tuberculin (0.1 to 
0.5 mg.) at intervals of three days. The advan- 
tage of this method is due to the fact that the 
diagnostic value of a reaction with a small dose 
of tuberculin exceeds the value of reactions with 
large doses. By this method, many patients are 
said to react with the first small dose while the 
cumulative action of subsequent doses results in 
a reaction in less susceptible individuals. 
Theories of Koch explained the tuberculin reaction by the 
ihf ReacSon" harmful or necrotic effect on the leucocytes and 
other tissue cells. The substances formed by the 
breaking down of these cells give rise to the fever 
and other symptoms. In tuberculous tissues this 
effect of tuberculin is much more marked. 



DIAGNOSIS. 



601 



Babes supposed that the increased susceptibility 
of tuberculous persons was due to a summation 
of effects of the products of the tubercle bacilli 
in the tuberculous focus and the injected tuber- 
culin. Von Pirquet and Schick explain the tuber- 
culin reaction as a phenomenon of allergy. This 
explanation is the most satisfactory one. (See 
Allergy.) 

In view of Naegeli's finding of tuberculosis, Limitations 
healed or active, in 97 per cent, of autopsies, the use J^ 1108 1C 
value of the tuberculin reaction would seem to be Tul,erc,llin - 
a relative one, and that the number of positive 
reactions obtained would depend on the amount of 
tuberculin used. 

Experience has taught certain limitations to the 
diagnostic value of tuberculin: 1. The test can 
not be applied to febrile cases inasmuch as the 
pre-existing fever could not be separated from that 
which the tuberculin might produce. 2. Cases of 
advanced tuberculosis frequently fail to give the 
reaction. The tissues of such patients have be- 
come resistant to the poison. 3. It is said that 
tuberculin frequently causes a similar reaction in 
those suffering from leprosy, actinomycosis and 
syphilis. Cornet and Meyer suggest that the 
phenomenon as it occurs in leprosy and actinomy- 
cosis is to be considered in the nature of a "group 
reaction" in view of the close relationship of the 
tubercle bacillus to actinomyces and Bacillus leprae. 
It does not always occur in syphilis, and in posi- 
tive cases a latent tuberculosis may be responsible 
for the reaction. By a number of writers the facts 
just stated are taken to indicate that the reaction is 
not of specific character; that it may often be ob- 
tained in the tuberculous by the injection of ap- 



602 INFECTION AND IMMUNITY. 

parently indifferent substances as trypsin, peptone 
(albumose), sodium cinnamate and the "mycopro- 
teins" of other bacteria provides additional sup- 
port to this view. On the other hand, since rela- 
tively large amounts of these indifferent sub- 
stances are required to produce the reaction, where- 
as minute amounts of tuberculin suffice, others 
hold that the specificity of the latter substance 
may be maintained. 

Early tuberculosis reacts to tuberculin in the 
most typical manner. On account of the fact that 
latent or healing cases may respond to the test, its 
positive outcome gives no indication of the serious- 
ness of the patient's condition, which is a practical 
question of some importance. 
Danger (H The fear that tuberculin, in producing an in- 
Tubercuiin. flammatory reaction around tuberculous areas, 
may cause a dissemination of the bacilli, has acted 
strongly in preventing the use of the toxin for 
both diagnostic and therapeutic purposes. On a 
priori grounds, such an event would seem to be a 
possibility, for, with the inflammation, the vessels 
surrounding the tubercles become congested, new 
leucocytes accumulate and there is an extravasation 
of fluid. Since during the subsidence of the in- 
flammation a certain number of leucocytes may 
again leave the area and as the extravasated fluid 
returns to the circulation, bacilli may be carried to 
other tissues by them. Contrary to such reasoning, 
however, the observations of Koch and his follow- 
ers in animal experiments and in the diagnostic 
and therapeutic use of tuberculin in man, lead 
them to say that tuberculin when properly ad- 
ministered never causes an aggravation or exten- 
sion of the disease. Similar conclusions were 






PIRQUET REACTION. 603 

reached by Trudeau, Baldwin and Kinghorn in 
animal experiments in which, "as in previous ob- 
servations, a favorable absorptive influence was 
noted on the diseased focus." Bearing in mind 
the limitations mentioned above, and the possibil- 
ity of the reaction being induced by leprosy, acti- 
nomycosis and syphilis ( ?), the statement of Osier 
may be quoted that "in obscure internal lesions, 
in joint cases and in suspected tuberculosis of the 
kidneys the use of tuberculin gives most valuable 
information." 

Von Pirquet made use of the increased capa- cutaneous 
bility of the skin of tuberculous patients to react v. Pirquet. 
to tuberculin as a means of diagnosis of tuber- 
culosis (see Anaphylaxis). The test is carried out 
as follows : The ventral surface of the forearm is 
cleansed with ether and two drops of old tuber- 
culin are placed on the skin at points about 10 cm. 
apart. The skin underneath the tuberculin is 
then scarified over an area about the size of a pin- 
head, as for an ordinary small-pox vaccination. A 
small quantity of cotton is then placed over the 
scarifications until they are dry. A third scarifi- 
cation is made about 10 cm. from one of the first 
two and no tuberculin used. This is to be used 
as a control. 

The ensuing reactions are described by v. Pir- 
quet as follows: 

1. Traumatic reaction: The vaccination and 
control sites show in a few minutes a small papule 
surrounded by a soft red areola which disappears 
in a few hours. There remains a small slightly 
raised pinhead-sized red spot which becomes cov- 
ered with a crust. This is succeeded by pigmenta- 



604 INFECTION AND IMMUNITY. 

tion and then a gradual return to normal within 
a week or two. 

2. Negative reactions show the same phenomena 
as the control site. The swelling lasts only 
twenty-four hours, and the areola is under 5 mm. 
in diameter. 

3. The positive reaction : (a) Incubation period, 
which lasts from three to twenty-four hours. In 
most cases the reaction is fully developed in 
twenty-four hours. Those developing later than 
twenty-four hours v. Pirquet calls "torpid/ 5 These 
torpid reactions occur more frequently in older 
than in young children and in clinically unsus- 
pected cases. It occurs in manifest tuberculosis 
only exceptionally. 

(b) Development: The inflammatory reaction 
begins usually with a slightly raised areolar red- 
dening which spreads from the scarification site 
and increases rapidly in diameter and height. The 
diameter of the papule is on an average about 1 
cm. but may reach 3 cm. Small vesicles may form 
on the surface of the papule. The color differs 
with the normal coloring of the skin; usually it 
is of a deep red color. Very pale papules some- 
times develop in cases of fatal tuberculosis (cach- 
ectic reaction). The border of the papule is some- 
times sharp, sometimes irregular and at times 
small papules may be found surrounding it. 

(c) Eetrogression. The maximum development 
is usually reached in forty-eight hours and after 
this the swelling declines and the red color changes 
to a violet, then to a yellow color and finally 
becomes brown. The swelling disappears usually 
in from five to eight days and the pigmentation 



P1RQUET REACTION. 



Value of 
the Reactio 



The 
Ophthalmic 



in a few weeks. The best time for a single obser- 
vation is 48 hours after the vaccination. 

(d) Secondary reaction : In cases giving a neg- 
ative reaction a second test may be followed by a 
positive reaction. In this case, the first vaccina- 
tion site may show a slight reddening. 

The cutaneous reaction is a very delicate one 
and many cases of healed tuberculosis give a posi- 
tive reaction. Since most adults, according to 
autopsy findings, have healed foci of tuberculosis 
the reaction as an indication of active lesions is 
of value only in children below the age of puberty. 

Various modifications of the v. Pirquet reaction 
have been devised but cannot be discussed here. 

Calmette proposed the instillation of tuberculin 
into the conjunctival sac as a diagnostic procedure Reaction, 
in tuberculosis. In negative cases this is followed 
by only a slight reddening. In positive reactions 
a more or less severe conjunctivitis follows. The 
reaction has not become popular owing to the pos- 
sibility of danger to the eye. 

The original unfavorable results which were ob- 
tained in the therapeutic administration of tuber- 
culin are referred by Koch, Petruschky and others 
to improper selection of patients. Those in a feb- 
rile condition and those in whom destruction of 
tissue is advanced are not suited for the treatment, 
and in them little or nothing is to be hoped from 
the administration of tuberculin. Its curative value 
is supposed to depend on the local inflammatory 
reaction which it causes around tuberculous foci, 
and perhaps also on the necrosis which Koch claims 
is caused in the tubercles themselves. It must be the 
object during the whole course of treatment to ad- 
minister the toxin in such doses that a moderate 



Taherculin 
Therapy. 



006 INFECTION AND IMMUNITY. 

or minimum local reaction occurs. Larger amounts 
which would cause febrile reactions and eventually 
render the patient resistant to tuberculin and thus 
preclude the local changes are to be avoided. It is 
customary to begin with 0.1 to 0.05 milligrams 
and gradually to increase the amount injected. 
If fever is caused by a particular dose, larger 
amounts are not to be given until fever ceases to 
follow this dose. By the time a dosage of 50 milli- 
grams is reached, which may require many months, 
the patient usually has lost the power of reacting 
and the injections are to be interrupted until Le 
again becomes sensitive to the toxin (from three 
to six months), after which treatment should be 
resumed. Cure is recognized when the patient Ills 
lost permanently the power to react, his condition 
then being identical with that of the healthy man. 

The principles on which the action of tuberculin 
depend are hypothetical. Marmorek says that the 
fever and local changes are due to a special toxin 
(the true toxin), which the bacillus secretes under 
the stimulation of the tuberculin. Ehrlich sup- 
poses that cells adjacent to the tubercles have been 
injured moderately by the tuberculin which is pro- 
duced in situ, and that as a consequence of this 
injury such cells are particularly susceptible to the 
additional tuberculin which is injected, and react 
to the stimulus by proliferation (Marx). In ac- 
cordance with this conception the fever also in 
some obscure way is related to the local reaction. 

It is probable that the therapeutic value of 
tuberculin depends on the utilization of the sub- 
cutaneous and other body cells as a source of anti- 
bodies. The formation of these antibodies follows 
the injection of tuberculin, whereas in the tuber- 



TUBERCULIN TREATMENT. 607 

culous process only the tissues directly involved 
are stimulated to antibody production. Koch pub- 
lished favorable results from the use of tuberculin 
but reports from other sources were less satisfac- 
tory. Koch's Neutuberculin (Bazillenemidsion) 
is used in a similar manner. Koch proposes to use Treatment 

• p ^ . , with TR 

the agglutinating power of the patient s serum as and "New 
an index of the immunity caused by the injection. 
The formation of agglutinins perhaps indicates in 
a general way the ability of the patient to form 
antibodies, but from the well-known fact that the 
agglutinating power does not go hand in hand with 
the protective power of serum in relation to many 
infections, this method of estimating the degree 
of immunity does not rest on a good basis. The 
agglutination reaction is carried on with the emul- 
sion which is used for immunization. Treatment 
in man is begun by the injection of 0.0025 mg. of 
solid substance and the amount is increased rap- 
idly every day or two until a reaction occurs with 
a temperature of from 1.5° to 2° C. After a pause 
of a week the injections are begun againand event- 
ually a dose of 20 mg. may be given. During 
treatment the agglutinating power of the patient's 
serum is tested frequently, and if it is not suffi- 
ciently high intravenous injection of the fluid por- 
tion of the emulsion may be practiced. The agglu- 
tinating power may go as high as from 1 to 25 to 
1 to 150, rarely 1 to 200 or 300. 

Following the work of Wright and Douglas, the 
•opsonic index has been used as a guide to the 
injection of preparations of tubercle bacilli. By 
the concentration of opsonins the state of immu- 
nity can be gaged and the dosage thus regulated 
as to time and amount. By means of this proce- 



Maragliano. 



608 INFECTION AND IMMUNITY. 

dure much valuable information has been obtained 
in regard to the avoidance of injections during the 
"negative phase" and the regulation of the size of 
the doses. 

It is still a disputed question as to whether 
the condition of the patient as an indication for 
tuberculin injection can best be judged by the 
clinical s}anptoms or by the estimation of the 
opsonic index. There is no question, however, 
but that in suitable cases the proper application of 
vaccine treatment in tuberculosis is a valuable 
therapeutic aid. 
serum of Maragliano publishes the following conclusions: 
(1) "It is possible to produce a specific (serum) 
therapy for tuberculosis; (2) It is possible to 
immunize the animal organism against tuberculo- 
sis as is done in other infectious diseases, and 
there is good reason for hope for an antitubercu- 
losis vaccination for man." He recognizes bacteri- 
cidal, antitoxic and agglutinating properties of the 
serum as normal defensive powers of the body, and 
says that these powers are increased as the result 
of immunization. The bactericidal power of the 
serum is determined by its ability to inhibit the 
growth of cultures of the tubercle bacillus; its 
antitoxic power by its ability to neutralize a test 
poison which is obtained from cultures by macerat- 
ing them in hot water; and its agglutinating 
power is tested with the homogeneous cultures of 
Courmont and Arloing. For the immunization of 
animals a soluble toxin prepared by the filtration 
of young cultures, and also the intracellular toxins 
which are extracted by water from killed virulent 
bacilli, are injected. By using both substances, 



ANTITUBERCULOSIS SERUM. 609 

antitoxic and other antibodies are said to be 
formed. 

The unusual claim is made by Maragliano that 
his antituberculosis serum is effective in the treat- 
ment of human tuberculosis not only because of its 
own properties, but because it causes the tissues to 
form additional antibodies. It is difficult to take 
the latter claim seriously, since it is not in accord 
with the laws of antibody formation as we under- 
stand them at the present time. However, favor- 
able reports of the value of the serum have been 
published principally from Italian sources. It is 
claimed that the serum manifests its curative pow- 
ers and causes an increase in specific antibodies 
when given per os. 

Maragliano also advocates a method of mixed Mixed fmmn- 

-. . . .... . t • t ization and 

active and passive immunization m man, m which vaccination. 
1 c.c. of serum is given subcutaneously every sec- 
ond day for twenty days; for a second period the 
same quantity of serum is given, but supplemented 
by increasing amounts of the toxic extract of 
bacilli; and for a third period the toxic extract 
is injected in increasing doses during from three 
to four months. 

The same authority thinks that it may be 
possible to vaccinate against tuberculosis by a 
single subcutaneous injection of a vaccine (killed 
bacilli?). He states that in both man and animals 
antibodies are formed in the serum following the 
vaccination, and that in animals their resistance to 
infections with living bacilli is increased. Mar- 
morek asserts that killed tubercle bacilli which 
have been treated with his antitoxic serum are 
readily absorbed from the subcutaneous tissue, and 
proposes the use of such bacilli as a vaccine. 



610 INFECTION AND IMMUNITY. 

serum of As stated above, Marmorek discredits tuberculin 
as the specific toxin of the bacillus. His "true" 
toxin is prepared by growing young and virulent 
bacilli ("primitive" bacilli) in a medium which 
contains leucotoxic serum, liver extract, glycerin 
and bouillon. The leucotoxic serum is prepared 
by immunizing calves with the leucocytes of 
guinea-pigs. Theoretical considerations which we 
need not detail suggested the use of this medium. 
The cultures are filtered after a few days of growth 
and the formation of tuberculin is avoided as much 
as possible. The immunization of horses with this 
filtered toxin yields the antitoxic serum of Mar- 
morek. Conflicting reports concerning its value 
are published from French sources. Schwartz an- 
nounces the complete cure of a case of tuberculosis 
of the larynx, and another of virulent tuberculosis 
of the conjunctiva and cornea by the exclusive use 
of M armor ek's serum. 
immpniza- Both Maragliano and Behring affirm that the 
Milk, immunizing substances are excreted in the milk of 
cows which have been strongly immunized against 
tuberculosis, and both have suggested that the use 
of such milk by infants may render them more re- 
sistant to tuberculosis. 

The agglutination reaction has been suggested 
by Courmont and Arloing and others as a means of 
diagnosis in tuberculosis. Others who criticise this 
idea affirm that agglutinins are not developed suf- 
ficiently in tuberculosis to render the test of 
value, and that the serum of normal man may be 
as highly agglutinating as that of the tuberculous. 
In view of the fact that the tubercle bacillus grows 
in coherent masses in ordinary cultures special 
manipulations are necessary to render it suitable 



BOVINE TUBERCULOSIS. Oil 

for the agglutination reaction. Courmont and Ar- 
loing prepare a homogeneous culture by first grow- 
ing the organism on a certain potato medium and 
then in glycerin bouillon, which is frequently 
shaken. The cells are said to be well isolated after 
this procedure. Koch uses his emulsion of pow- 
dered bacilli for the test. The serum of man or 
animals as a result of immunization may reach an 
agglutinating power of 1 to 2,000 exceptionally 
(Maragliano). 

APPENDIX TO TUBERCULOSIS. 

TUBERCULOSIS AND PSEUDOTUBERCULOSIS IN ANIMALS. 

Certain differences between the bacilli of human and Bovine 
bovine tuberculosis were mentioned in the preceding Tuberculosis. 
section. In cattle the disease shows a characteristic 
tendency to remain localized in one organ or group of 
organs over a long period. It is a nodular disease as in 
man, but differs from human tuberculosis in that no- 
dules often grow to large size, may be imbedded in and 
sharply differentiated from surrounding healthy tissue, 
and not infrequently involve serous surfaces, forming 
large masses of firm sessile or pedunculated tumors. 
The nodules frequently are fibrous from the beginning, 
undergo early and extensive calcification and rarely 
soften. We are not to understand, however, that miliary 
tuberculosis does not occur in cattle. Although the 
process in the lungs is usually of a fibrous and large 
nodular nature, rapid dissemination with formation of 
many miliary tubercles may cause the picture of acute 
tuberculous consolidation in a certain number of cases. 
According to the statistics of Ostertag, based on 43,000 
cases of bovine tuberculosis, localization is as follows: 
Lungs, 75 per cent. ; pleura and peritoneum, 50 per 
cent. ; peribronchial glands, 60 per cent. ; spleen, 40 per 
cent. In more or less generalized cases the lungs are in- 
volved in 100 per cent, of the cases; serous membranes^. 
90 per cent. ; liver, 85 per cent. ; digestive tract, 00 pel- 
cent. ; spleen, 50 per cent.; kidneys, 30 per cent.; mouth- 
cavity, 5 per cent. In cows the uterus, in general infec- 
tion, is involved in 65 per cent, of the cases, the udders 
in from 5 to 10 per cent., and the ovaries in 5 per cent. 
It seems that the lungs are the most common infection 



612 INFECTION AND IMMUNITY. 

atrium, and transmission probably is accomplished chief- 
ly through the secretions of the respiratory passages. 
In the udders the process may at first be one of miliary 
tuberculosis, but a large amount of fibrous tissue forms 
in time, many acini are transformed into retention cysts, 
in which tubercle bacilli, free or intracellular, may be 
present in large numbers. 

Aside from anatomic changes and clinical symptoms, 
diagnosis depends on the tuberculin reaction, and, in 
relation to the udder, the demonstration of bacilli in the 
milk by staining methods or inoculation into guinea- 
pigs. 

The tuberculin reaction in cattle is similar to that in 
man and is subject to the same general limitations, but 
is used extensively with the most satisfactory results. 
The complete elimination of tuberculosis from herds of 
cattle is possible, by using tuberculin as a diagnostic 
test, the slaughtering of infected animals, and the dis- 
infection of stalls. 

Tuberculosis among sheep and goats is rare. It occurs 
occasionally in the horse, hog and dog, and with more 
frequency in the cat. 
Avian ^ form of tuberculosis is very common in the chicken, 
Tuberculosis, and attacks also the pheasant, dove and turkey. The 
duck and goose are exempt from it. Although the or- 
ganism resembles that of human tuberculosis in size, 
staining properties and other general characteristics, 
differentiation is accomplished by means of the follow- 
ing points: 1. The avian bacillus shows a greater tend- 
ency to pleomorphinism as shown by club-shaped forms, 
unstained vacuoles, "spore-like -5 bodies, and branching 
threads. 2. It has a greater affinity for aqueous anilin 
dyes. 3. Growth takes place in artificial media more 
rapidly and on solid surfaces is characterized by its 
moist appearance and mucus-like consistence in contrast 
to the dry, warty, brittle growth of the human bacillus. 
4. The optimum temperature for growth (from 40° to 45° 
C. ) is several degrees higher than that of the mamma- 
lian organism. 5. Its pathogenicity for guinea-pigs is 
less and for rabbits greater than that of the human and 
bovine bacilli. Their difference in pathogenicity is 
further shown by the difficulty which is met in trying to 
infect fowls with the human bacillus. By varying the 
conditions of cultivation and by animal passage the two 
may be made to resemble each other very closely, al- 
though the permanent transformation of the human into 
the avian, or vice versa, has not been accomplished. 



_ 



TUBERCULOSIS OF FISH, ETC. 



613 



The disease attacks especially the intestines, mesen- 
tery and liver, in which are found hard, yellowish-white 
nodules, often rich in lime salts, and varying in size 
from that of a pea to that of a walnut. These condi- 
tions suggest the intestines as the infection atrium. The 
foci are rich in bacilli and histologically show the es- 
sential characteristics of tuberculosis. 

"Bacillus tuberculosis piscium" is the name given to Tuberculosis 
an acid-fast organism resembling the tubercle bacillus of Fish, Etc. 
which was cultivated from an inflammatory tumor in 
the abdominal wall of a carp. It grows well at low tem- 
peratures, the optimum being 25° C, is found in large 
numbers in the lesions within giant cells, and is dis- 
tinctly pathogenic for frogs. Certain authors state that 
the human bacillus when inoculated into the frog under- 
goes changes in its cultural and pathogenic characteris- 
tics, eventually resembling the organism cultivated from 
fish. 

Similar bacilli have been cultivated from a form of 
tuberculosis in the turtle (Friedman), and Blindsch- 
leiche — blind worm (Moeller). 

OTHER ORGANISMS RESEMBLING THE TUBERCLE BACILLUS. 

Certain other organisms of low pathogenicity resemble 
the tubercle bacillus in their acid-fast properties, their 
ability to grow in the form of branching threads, and to 
produce tubercular or nodular infections of a local na- 
ture in animals. They may be placed in a group which 
includes the tubercle bacillus. 

C. Fraenkel, also Neufeld, recognize in smegna two 
acid-fast bacilli, calling one "tuberculoid" because of its 
morphologic resemblance to the tubercle bacillus, and the 
other "diphtheroid" since it shows the pleomorphism of 
the diphtheria bacillus. One of these organisms may be 
identical with the "syphilis bacillus" of Lustgarten. 
Smegma bacilli are most numerous beneath the prepuce 
in man and about the clitoris and vulva in women. 
Their chief significance lies in the danger that they may 
be mistaken for tubercle bacilli in suspected cases of 
genitourinary tuberculosis. Smegma bacilli may readily 
enter the urethra in women and be carried into the blad- 
der during catheterization or cystoscopic examination. 
In man the danger of bacteriologic error may be elimi- 
nated largely by cleansing the glans and carefully irrigat- 
ing the urethra. Urine which is then passed is not likely 
to contain smegma bacilli (Young and Churchman). 



Smegma Bac- 
illus and the 
Bacillus of 
L,astgarten. 



614 INFECTION AND IMMUNITY. 

Bacilli from "Milk bacilli" and "butter bacilli" are acid-fast or- 
Milfc, Batter ganisms resembling the tubercle bacillus morphologi- 
a " Grass- ca Uy # j n injecting milk into guinea-pigs as a test for 
tuberculous contamination, Petri occasionally noted, as 
a consequence, a thick membranous growth which en- 
cased the liver and spleen and bound the coils of intes- 
tines together. The omentum was thickened, and this 
structure and the mesenteric lymph glands contained 
nodules. In pure culture the organism is pathogenic for 
guinea-pigs only when given in large doses, and may kill 
the animals in several weeks with the anatomic changes 
noted above. Its virulence is increased by the simul- 
taneous injection of butter. It is not pathogenic for 
man ( Herbert ) . 

Moeller cultivated organisms resembling the tubercle 
bacillus from timothy (timothy bacillus), from manure, 
and a third (grass bacillus II) from the dust of a 
manger. The last is marked with great pleomorphism, 
thread formation and motility in young cultures. 

The leprosy bacillus and the B. of Lustgarten which 
resemble the tubercle bacillus will be considered later. 

PSEUDOTUBERCULOSIS IN ANIMALS. 

Although some of the organisms described above are 
often called pseudotubercle bacilli, the term pseudo- 
tuberculosis is now applied somewhat specifically to a 
nodular disease occurring in rats, mice and sheep (and 
perhaps in other domesticated animals), and in which 
organisms differing from the tubercle bacillus in stain- 
ing and culture properties, morphology and pathogenic- 
ity, are found. The clinical course and anatomic 
changes are similar in the three animals mentioned, al- 
though the organisms are different. The lymph glands 
near the infection atrium become enlarged chiefly by a 
cellular infiltrate rather than extensive proliferation of 
fibrous tissue. The nodules undergo a soft caseation 
very early and rarely show calcification. The infection 
finds its way to other sets of lymph glands and may be- 
come more or less generalized with the formation of 
smaller and larger sized nodules. 
Rats and Pseudotuberculosis of rodents, occurring spontaneous- 
Mice, ly in rats, guinea-pigs, rabbits and cats, is caused by an 
organism of considerable pathogenicity, and may occur 
in epidemic form in laboratory animals. Chickens also 
may contract the disease. Intraperitoneal inoculations 
in guinea-pigs are fatal in a few days. Spontaneous in- 
fection takes place through the intestinal tract, and re- 
gional organs show the principal changes. The liver and 



LEPROSY. 615 

spleen contain many nodules which may be as large as 
a hazelnut, and which are frequently caseated in the cen- 
ter. The organism is called Bacillus pseudotuberculosis 
rodentium or Streptobacillus pseudotuberculosis dor. 

The disease in mice is caused by a diphtheria-like or- sheep. 
ganism called Bacillus pseudotuberculosis murium and 
is pathogenic especially for the gray mouse. 

A similar infection in sheep is of more importance and 
occurs with some frequency. It is called pseudotubercu- 
losis ovis, and the bacillus has a corresponding name. 
The organism is supposed to gain entrance through 
wounds in the feet and legs, following which the adja- 
cent lymph glands become involved, and the infection 
may be transferred to the lungs and other organs 
through the lymphatic circulation. The lesions are 
nodular, of varying size, usually surrounded by a fibrous 
capsule, and are either semipurulent or undergo early 
caseation. They may be found in all the visceral or- 
gans. 

An organism resembling that cultivated from the 
sheep has occasionally been found in nodular conditions 
in cattle. 

II. LEPROSY. 

Leprosy existed in Egypt in prehistoric times course of 
and extended to other lands only when inter- 
course was established. It reached Greece at 
about 345 B. C, Italy in the first century 
before Christ, and from the latter country 
extended to Germany, France and Spain. Cru- 
saders returning from the Orient also brought back 
the disease in later times and eventually all 
Europe was infected. Leprosy is known to have 
existed in Great Britain in the tenth century, and 
from that country it was carried to Iceland and 
Greenland. From Germany it extended to the 
Scandinavian countries, and from the latter to 
Finland and Eussia. It also reached Eussia from 
the South and East, and in the South it was at 
one time called the Crimean disease. The West 
Indies and South America probably were infected 



610 INFECTION AND IMMUNITY. 

from Spain, and through these channels the disease 
was carried to the southern states. The leprosy of 
the western states seems to have been imported by 
Norwegian immigrants chiefly. In 1902 the 
United States leprosy commission found 278 cases 
in this country. One hundred and eighty-six of 
these individuals probably contracted the disease 
in this country, 120 were born in foreign coun- 
tries and 145 were native born. The disease also 
extended around the globe in the opposite direc- 
tion, reaching China, Japan and the East Indian 
islands from India. The Sandwich Islands be- 
came infected in the nineteenth century. 

The contagiousness of the disease appears to 
have been recognized at a very early period. In 
636 A. D. leprosy houses were instituted in Italy 
and other countries, and the practice of segregat- 
ing lepers soon became general. The hospitals 
were called Lazarus houses in middle Europe and 
St. George houses in Scandinavian countries. 
Pipin and Charles the Great declared marriage be- 
tween lepers illegal. The rapid disappearance of 
leprosy in middle Europe during the sixteenth 
century is ascribed largely to the segregation of 
the patients. 
Bacillus of In 1872 Hansen announced that small rods, 
sometimes intracellular and sometimes free, were 
to be found constantly in teased preparations of 
leprous tissue. These rods, leprosy bacilli, are 
now universally recognized as the cause of the 
disease, and in 1879 they were stained by Neisser 
and a year later by Hansen. The organism is non- 
motile, has about the dimensions of the tubercle 
bacillus, the same staining reactions, and fre- 



LEPROSY BACILLUS. 617 

quently shows a beaded appearance (degeneration 
forms ? ). It is said to take up dyes more readily 
than the tubercle bacillus, but the difference is not 
so great as to be distinctive. It stains by Gram's 
method. 

Duval has recently succeeded in cultivating the 
leprosy bacillus on media prepared as follows : 

The rind was carefully removed from the fruit portion cultivation 
of fully matured green bananas, every precaution to 
avoid contamination being used, and large blocks of the 
fruit, after slanting one surface with a sharp knife, were 
introduced into suitable sterile glass cylinders provided 
at the bottom with cotton plugs saturated in sterile dis- 
tilled water. These plugs served not only as support for 
the banana, but as a source of constant supply of mois- 
ture. Sterile 1 per cent, solutions of tryptophan, cystein 
(made from protein), and leucin were next prepared and 
a portion of each poured on and allowed to saturate the 
banana. These solutions were used separately and in 
varying combinations, in order to determine on which 
the B. leprw would grow best or grow at all. Both the 
banana and agar, which was saturated in a 1 per cent, 
solution of cystein, proved an excellent medium for the 
artificial cultivation of the leprosy bacilli when incu- 
bated at from 32 to 35 degrees C. The maximum growth 
occurred at a temperature of 32 degrees C. Light seems 
to favor the growth of B. leprce; cultures kept in a glass 
incubator regulated at 32 degrees C. grew more rapidly 
than those in the dark chamber under similar conditions. 
Multiplication began early in the transplants and visible 
growth developed in the form of small, glistening, white 
colonies in from four to six weeks. Growth also occurred 
on the banana and agar when a solution of cystein and 
tryptophan had been added. The fact that growth 
occurred on the protein-cystein medium, and not on the 
others except in the presence of it, shows very conclu- 
sively that B. leprw utilizes the end-products of digestion 
and not the products of cell metabolism. At least it is 
reasonable to assume that this is the case, if deductions 
may be drawn from these experiments. Multiplication 



618 INFECTION AND IMMUNITY. 

in vitro of an acid-fast organism was obtained from the 
transplanted leprosy tissue on the above mentioned media 
from four cases of leprosy which corresponded in every 
essential to the leprosy bacillus. Not only did the 
leprosy bacilli develop in the original cultures but they 
continued to grow in subcultures. That the artificial 
growth is B. lepra' there can be no doubt, as the morpho- 
logic and cultural features and the animal tests have 
clearly proved. 

Lugai has shown that the leprosy bacillus is 
pathogenic for Japanese dancing mice. The ba- 
cilli not only multiply at the site of inoculation 
but become disseminated throughout the body, 
producing lesions having the typical characters of 
leprous lesions in man. Xicolli is said to have 
produced leprous nodules in monkeys by inocu- 
lating them with diseased tissue, and finally Duval 
has produced typical leprosy of the tubercular type 
in the monkey (Macacus rhesus), by means of pure 
cultures of leprosy bacillus. 

So far as known, the organism has no natural 
existence outside the human body, and it is dis- 
seminated only by the secretions of the diseased. 
It is discharged chiefly through the secretions of 
the nose and the upper respiratory passages, the 
surfaces of which are so commonly the seat of lep- 
rous ulcers, and also through ulcerating lesions of 
the skin. Expectoration, sneezing and coughing 
have approximately the same significance for the 
dissemination of leprosy bacilli as of tubercle ba- 
cilli. However, the organisms which are found in 
the sputum and nasal secretions appear to be 
largely degenerated, a condition which may lessen 
Transmission, the infectiousness of these substances. 

The infectiousness of the leprosy bacillus is of a 
low character. "Epidemiologic experience teaches 



Atria. 



TRANSMISSION 619 

that infection occurs only through intimate and 
prolonged association with the diseased, in which 
doubtless uncleanliness plays a very important 
role"' (Gotschlich). A leprous husband eventually 
infects his wife, and the children of lepers com- 
monly develop the disease early in life. The high 
percentage of leprosy which is noted among the 
laundresses of infected localities indicates that the . 
disease may also be transmitted by indirect contact. 
Gotschlich throws some doubt on the importance 
of dust infection since so many of the bacilli found 
in sputum appear to be degenerated. Nothing is 
known of the resistance and viability of the organ- 
ism outside the body. 

On account of the early appearance and almost infection 
constant occurrence of leprous lesions in the nasal 
passages Strieker believes that the latter constitute 
the chief infection atrium; of this Hansen is not 
positive. Nasal ulcers may be present in latent 
or apparently healed cases. Kolle cites a case show- 
ing extensive involvement of the spleen and liver 
in which the intestinal tract was considered the in- 
fection atrium. In some instances in which the 
disease is first noted in the feet, the organisms 
are supposed to gain entrance with infected soil 
through abrasions in the skin. According to Cor- 
nii and Babes, infection may take place through 
the hair follicles and sebaceous glands. The theory 
of Jonathan Hutchinson that leprosy may be con- 
tracted through eating diseased fish, or that the lat- 
ter in some way may render individuals susceptible 
to infection is not now credited. Hereditary 
acquisition of the disease is of doubtful occur- 
rence, although the bacilli have been found in ova 
(Babes) and commonly are present in enormous 



of Bacilli. 



(>20 INFECTION AND IMMUNITY. 

numbers in the testicles. Hansen states, however, 
that he has never found them in the female gen- 
erative organs. 
Location The presence of lar^e masses of bacilli in leprous 
tissues is a characteristic of the disease. To a large 
extent they are intracellular and they are often 
grouped in such a way as to resemble bundles of 
cigars. Hansen believes that the bacillus is essen- 
tially an intracellular parasite, and that it becomes 
extracellular only as a result of degeneration and 
disintegration of infected cells. Unna, on the 
other hand, considers their location in lymph 
spaces as most characteristic. They appear to be 
carried to distant parts through the lymphatics. 
Certain large .vacuolated cells, the lepra cells of 
Virchow, the globi of Hansen, which are filled to 
bursting with the leprosy bacilli, are characteristic 
of the disease. Unna and others consider these 
bodies as zooglear masses rather than as intracel- 
lular accumulations, and Kanthack interprets them 
as bacillary thrombi in the lymphatic vessels. The 
nodules, or lepromas, consist of granulation tissue, 
containing many round and epithelioid cells, lepra 
cells and occasional multinuclear giant cells. In 
cutaneous macules columns of round cells surround 
the blood vessels, there is some proliferation of 
epithelioid cells, but relatively few bacilli. The 
bacilli are most numerous in the nodular lesions. 
They are found in the Glissonian tissue of the liver, 
in the pulp and follicles of the spleen, in the glom- 
eruli and interstitial tissue of the kidneys when 
these organs are involved, in the nerves in both 
the nodular and maculoanesthetic forms of the 
disease, and in the vascular endothelium. They 
have been demonstrated often in the ganglionic 



LEPROSY BACILLUS. 621 

cells of the posterior root ganglia. Their occur- 
rence in these cells leads Metchnikoff to say that 
the latter have phagocytic properties 

In view of the chronic course of leprosy and the Elldotoxil * < ? )« 
absence of signs of intoxication over considerable 
periods, it seems probable that the bacillus secretes 
little or no soluble toxin. From time to time, how- 
ever, patients with tubercular leprosy develop fever, 
which may persist for weeks or months and event- 
ually terminate in death. During such attacks 
the nodules not infrequently enlarge, become soft 
and later disappear. Lie conceives that such 
periods represent massive infection of the blood 
with the bacilli, and that at this time the latter 
undergo extensive disintegration and liberate en- 
docellular toxins to which the toxic phenomena are 
due. It is a remarkable fact that intercurrent in- 
fections, as measles and smallpox, and the adminis- 
tration of potassium iodid, cause a similar enlarge- 
ment, softening and final disappearance of leprous 
nodules, accompanied by marked degenerative 
changes in the bacilli. Hansen is of the opinion 
that the fever induced by these conditions has an 
actual curative effect, although its influence is not 
readily analyzed. He quotes the opinion of Dan- 
ielssen that potassium iodid may be used to deter- 
mine the cure of leprosy, which would be indicated 
by absence of a febrile reaction. 

General confidence is not felt in the "leprolin" 
which Eost prepared from his cultures of the lep- 
rosy bacillus (?). His cultures are said to have 
been mixtures of micro-organisms. 

Because of the failure until recently to cultivate !mty P £md 
the leprosy bacillus, experimental work with the Defense* 



022 INFECTION AND IMMUNITY. 

serum and cells of man and animals, by which 
conclusions as to the defensive powers of the body 
might be drawn, can not be carried out. It seems 
probable that all men are susceptible to leprosy 
under the proper conditions. Sauton states that 
children of from 4 to 5 years are particularly 
liable to infection. Other conditions which may 
increase suspectibility are of a conjectural nature. 
It is possible that leprosy predisposes to tuber- 
culous infection. 

The condition in leprosy seems to be that of an 
organism of low virulence against which the body 
possesses no decisive protective agency. The reac- 
tions for the most part are of a local nature, involv- 
ing the proliferation of connective tissue and blood 
vessels, and the accumulation of lymphocytes. That 
phagocytosis by macrophages (lymphocytes, con- 
nective tissue, endothelial and ganglionic cells) is 
a factor which antagonizes the proliferation of the 
bacilli is suggested by the large number of bacilli 
which are found in these cells. 
prophylaxis. The principles of prophylaxis may be illustrated 
by citing the practices in Norway. Originally all 
lepers were confined to institutions. At the pres- 
ent, however, only indigent lepers and those who 
can not be suitably cared for at home are required 
to enter an asylum, where they live under the best 
hygienic conditions. Other patients are allow r ed to 
remain at home, with the understanding that they 
sleep alone and, if possible, have separate rooms, 
that their clothing, linen and eating utensils be 
used by no one else, and that proper precautions 
be taken in the washing of linen. Dressings and 
bandages must be burned. Under these regulations 



of the 
Disease. 



GLANDERS. 623 

the number of lepers in Norway has decreased from 
2,870 in 1856 to 577 in 1900. Banishment to the 
Island of Molokai is practiced in the Sandwich Is- 
lands. Segregation of lepers should be brought 
about in this country. 

Carasquilla attempted the production of an anti- 
leprosy serum by immunizing horses with the blood 
of leprous patients. Although a few favorable re- 
ports concerning its effects appeared it has not 
proved of value in the hands of others. 

III. GLANDERS (FARCY). 

Under natural conditions the horse is the chief occurrence 
sufferer from glanders or farcy, the former name 
being applied to the disease as it occurs in the nose, 
the latter when in the skin. These names are relics 
of the time when the two forms of the disease were 
not recognized as having a common etiology. In 
either locality the disease may be acute or chronic, 
and in the horse about 90 per cent, of the cases 
are chronic. The ass is occasionally infected, and 
in this animal, as well as in man, an acute general 
infection (bacillemia) frequently develops, in ad- 
dition to the cutaneous and nasal lesions which 
characterize the disease. Fortunately, glanders in 
man is rare. Cows and rats are immune, or nearly 
so ; the sheep, goat and dog have fairly high resis- 
tance, although they may be infected artificially; 
the dog and rabbit are moderately susceptible, and 
for the guinea-pig and members of the cat family 
(tiger, lion and leopard), the bacillus is very vir- 
ulent. Infection of the last-named animals has 
been noted in menageries as the result of feeding 
them with the meat of a horse which had died of 
glanders. The acute infection usually is fatal, and 



024 INFECTION AND IMMUNITY. 

complete recover}- from the chronic form of the dis- 
ease is infrequent. Something less than 50 per 
cent, of the chronic infections in man terminate 
in recover}'. 
Baeiiins The specific microbe. Bacillus mallei, discovered 

Mallei. 

in 1882 by Loeffler and Schiitz, is an aerobic or- 
ganism which has approximately the morphology 
and size of the tubercle bacillus, but lacks the acid- 
fast property of the latter. It stains with anilin 
dyes, especially carbol fuchsin, but not by Gram's 
method. "With weak staining it shows a granular 
structure. It grows well on ordinary culture media, 
showing a characteristic appearance on potato. In 
unfavorable media it may produce threads, while 
under more favorable conditions coccus-like forms 
are seen. Marked involution forms occur on media 
containing 3 per cent, of sodium chlorid 
(Wherry). The optimum temperature for growth 
is from 30° to 40° C. 
Resistance ^he bacillus is only moderately susceptible to 
toxin, sunlight, by which it is killed in about twenty-four 
hours. It withstands freezing, lives for two or 
three weeks in a dried condition at room tempera- 
ture, and is killed by a temperature of from 56° to 
60° C. in from ten minutes to one and one-half 
hours, depending on the amount and character of 
the medium in which it lies. Its resistance to the 
ordinary disinfectants (corrosive sublimate, car- 
bolic acid, etc.), is not high. Milk of lime and 
solutions of calcium chlorid are suitable for the dis- 
infection of stalls. In culture media the organism 
secretes no soluble toxin, but it contains an endo- 
toxin which probably is one of the constituents in 
the various preparations of mallein„ 



MALLEIN. 



625 



The method by which the mallein of Boux and Preparation 

J of Mallein. 

iSTocard is prepared is identical with that used in 
the preparation of the old tuberculin. A virulent 
strain of the glanders bacillus is allowed to grow 
for some time (from two weeks to two or three 
months) in bouillon which contains from 4 to 5 
per cent, of glycerin, the culture is then sterilized 
by heat and the bacteria removed by filtration. 
The toxin is not destroyed by high temperature. 
Other preparations, also called mallein, are made 
by extracting ground-up bacilli with a solution of 
glycerin and water (Helman, Kalning), or with 
water alone (Kalning and others) ; by killing a 
liquid culture of the bacillus (Bromberg) ; or by 
precipitating bouillon filtrates with absolute alco- 
hol (de Schweinitz and Kilbourne), or with am- 
monium sulphate or magnesium sulphate. The 
dry powders "morvin" and "dried mallein" are 
prepared by one or another of these precipitation 
methods. 

Glanders bacilli are found only in the tissues Distribution 

-, ,. P -i . t .-i*' -in -i of Bacilli and 

and secretions oi diseased animals, and the nasal infection 
discharges of the latter are the chief means of con- Atria - 
taminating feed, water and stables through which 
the disease usually is carried to other animals. 
The glanders bacillus does not readily penetrate 
the. intact skin and mucous membranes, although 
occasionally it may gain entrance through the hair 
follicles or sweat ducts. In the presence of even 
slight defects in these surfaces, as those caused in 
the mouth or nostrils of horses by hay or other 
food, infection readily occurs. According to No- 
card, invasion takes place commonly through the 
gastrointestinal tract following the ingestion of in- 
fected feed or water. Although involvement of the 



626 IXFECTION AND IMMUNITY. 

intestines and adjacent tissues frequently results, 
the organisms may become generalized, causing the 
disease in the nose, skin or other organs, without 
the establishment of foci in the intestines. 

In man infection occurs chiefly through abra- 
sions in the skin, and perhaps also through the 
nose, to which the bacilli have been carried by 
soiled ringers or other means. In experimental 
work with glanders extreme care is necessary as 
infection occurs very easily. Glanders has been 
transmitted to animals by rubbing bacilli on the 
intact skin. Several cases of acute glanders, end- 
ing fatally, have occurred in laboratory workers as 
the result of accidental inoculation. There appears 
to be little clanger to man in eating the meat of 
horses in which the disease was localized, pro- 
vided the meat has been well cooked. Such meat 
was fed to soldiers in one instance with no ill 
results. 
ReaJtnTns*! Variations in the course of the disease and in the 
intensity of the pathologic changes in different 
cases probably depend on variations in the resist- 
ance of the host and in the virulence of the para- 
site. In acute general infections in man, follow- 
/ ing an incubation period of from two to five days, 
during which the point of inoculation becomes vio- 
lently inflamed, a severe febrile condition develops, 
which is accompanied by general pains, swollen 
joints, a macular eruption, and often muscular and 
subcutaneous abscesses. In a short time nodules 
and indurated cords, made up of a leucocytic exu- 
date, edematous fluid and proliferating connective 
tissue cells, form in the subcutaneous lymphatic 
channels, and mark the progress of the infection 



L. 






PROTECTIVE PROCESSES IN GLANDERS. 627 

toward the lymph glands. The nodules, and also 
the cords, commonly undergo softening, and ab- 
scesses form and rupture through the skin. Nod- 
ules similar to those in the skin develop in various 
organs of the body; in the nose they break down 
and constitute ulcers. In chronic infections the 
lesions are of the same nature, although they evolve 
more slowly and tend to remain limited to particu- 
lar regions. Nasal, pharyngeal, tracheal or pulmon- 
ary glanders are forms of the disease which are en- 
countered in the horse. Connective tissue develop- 
ment is more marked in chronic than in acute 
glanders, although the peculiar liquefaction, sup- 
puration and ulceration of the lesions occur in the 
former as well as in the latter. Moderate leucocy- 
tosis is found in the blood (12000-14000). 

The nature of the pathologic changes found in Protective 

Processes 

glanders, the frequent chronic and the progressive 
course of the disease, and the fact that infection 
does not confer distinct immunity, are conditions 
which ally glanders closely to tuberculosis, 
pseudo-tuberculosis and leprosy. The essential 
lesion is the "infectious granuloma," and it is prob- 
able that the new connective tissue which is formed 
is to no small extent a factor in limiting the exten- 
sion of the infection. Nodules of glanders fre- 
quently are isolated by the surrounding reaction, 
the centers caseate and the contents eventually are 
discharged through the skin; cicatrization and 
healing in many lesions follow evacuation. Phago- 
cytosis of the bacilli by the epithelioid cells and leu- / 
oocytes in the nodules is said to be rather extensive. 
Agglutination of glanders bacilli takes place in 
high dilution with the serum of horses affected 
with glanders. An agglutination with serum in 



Mai 



628 INFECTION A.ND IMMUNITY. 

1 to 500 dilution is a valuable aid to diagnosis. 
Normal horse serum is said to agglutinate glan- 
ders bacilli at times in 1 to 250 dilution. Agglu- 
tination in dilution of 1 to 5,000 and 1 to 10,000 
has been observed. By active immunization of 
animals an agglutinating serum may be obtained, 
and such a serum may be used for the diagnosis 
of glanders bacilli. Precipitins are also formed. 
semm Treatment of danders with immune serums has 

Therapy anil f 

use of not been successful. Such treatment has been at- 
tempted with scrum prepared by immunization 
with mallein (Semmer). and with the serum of 
diseased animals (Hell and Toeper). The value 
of mallein in the diagnosis of glanders or farcy is 
similar to that of tuberculin in tuberculosis. Al- 
though it causes a rise in the temperature of nor- 
mal animals when given in considerable doses, the 
reaction produced in infected animals is so much 
more intense, and occurs with such smaller doses, 
that it is generally considered as specific in nature. 
Some doubt, however, has been thrown on the spe- 
cificity of the reaction from the facts reported by 
various observers that toxic substances from other 
organisms, as tuberculin and preparations from 
the pneumobacillus of Friedlander, Bacillus 
pyocyaneus, etc., cause similar phenomena in ani- 
mals suffering from glanders. Wladimiroff asserts, 
however, that the reactions caused by these sub- 
stances differ from that of maliein. 

For diagnosis a dose must be used which causes 
no reaction in a normal animal, and this varies 
with different preparations. The typical reaction 
has two essential components: 1, A rise in tem- 
perature which begins in from six to twelve hours 



ACTINOMYCOSIS. 629 

after the injection, reaches its maximum (from 40° 
to 42° C.) in from six to eight hours later, where 
it remains for a few hours, then gradually sinks, 
only to recur on the second day ; 2, an edematous 
and inflammatory tumor at the point of injection, 
which begins in from six to eight hours, and runs 
its course in from three to eight days, ending in 
resorption (Wladimiroff). Veterinarians gener- 
ally agree that mallein is a valuable diagnostic 
agent. Mallein also has been used in the treatment 
of glanders, but with rather doubtful results. 

Bacteriologic diagnosis is accomplished by culti- 
vating the bacilli from the abscess or secretions and 
testing the virulence of the culture by animal ex- 
periments (guinea-pig). 

IV. RHINOSCLEROMA. 

(See page 572.) 

V. ACTINOMYCOSIS. 

Actinomycosis is a chronic infectious disease of 
man and animals, the lesions of which present, 
characteristically, a central mass of purulent and 
necrotic material containing colonies of "ray 
fungi," about or through which is disposed an 
abundant growth of granulation or fibrous tissue. 
In young or rapidly progressing lesions the amount 
of purulent material is large, while in older lesions 
well formed connective tissue is more conspicuous. 
The disease prevails especially among cattle, al- 
though it is met occasionally in the horse, hog, 
sheep, dog, cat and other animals ; man is infected 
not infrequently. 

Although fungous threads had been found in 
diseases resembling actinomycosis in 1845 and 



G30 INFECTION AND IMMUNITY. 

later, Bollinger, in 1877. gave the first accurate de- 
scription of the disease in cattle, and in 1878 J. 
Israel described it as a new disease in man. A 
short time later Ponfick demonstrated the identity 
of bovine and human actinomycosis. 

The specific organism. Actinomyces bovis et 
liominis, on culture media consists of a mass of del- 
icate threads which exhibit "true branching" and 
which, to a certain extent, segment to form 
"spores." The radially arranged groups of cells 
which occur as somewhat characteristic sulphur- 
yellow macroscopic granules in the pus of the actin- 
omycotic abscesses, and which give to the organ- 
ism the name of "ray fungus," are essentially a 
manifestation of parasitic existence, although col- 
onies developing on media which contain serum 
or ascitic fluid may show a degree of "club" for- 
mation (Wright). Each granule represents a col- 
ony of organisms the members of which possess 
club-shaped extremities, and in the center of the 
mass and extending from it are many of the deli- 
cate threads found in cultures of the organism. It 
grows on various culture media, often as a mold, 
and stains by Gram's method. 
Resistance. The actinomyces is an organism of considerable 
resistance. Cultures remain alive for one year or 
more when in a dried condition and the spores in 
one instance germinated after having been pre- 
served for six years. A temperature of 80° C. 
for fifteen minutes kills the spores (Berard and 
Nicolas). When suspended in bouillon, spores are 
killed in fifteen hours by direct sunlight, but when 
thoroughly dried, approximately ten days' expos- 
ure produced no injury. 



ACTINOMYCOSIS. 



631 



Attempts to place the actinomyces in a botanic 
system have resulted in many differences of opin- 
ion. By some investigators they are considered as 
an independent family midway between the hy- 
phomycetes and the schizomycetes (bacteria), oth- 
ers place them under the hyphomycetes in the group 
of the streptothrix, while still others consider them 
as pleomorphous bacteria, placing them in the 
group cladothrix. Petruschky recognizes acti- 
nomyces, streptothrix, cladothrix and leptothrix as 
genera in the family trichomyces, the latter belong- 
ing to the order hyphomyces. Biological variations 
which have been encountered have led to the rec- 
ognition of several species of actinomyces, among 
which are a number of non-pathogenic forms. 
Wright limits the term actinomyces to those strains 
which produce colonies of club-shaped organisms 
in animal tissues. 

Many attempts have been made to transmit 
actinomycosis to animals by inoculating them with 
the diseased tissues of animals and man, and with 
pure cultures obtained from these tissues. Al- 
though a number of experimenters have reported 
positive results, the attempts usually have been 
fruitless. Probably Wright has been more success- 
ful than others in producing actinomycotic lesions 
in rabbits and guinea-pigs by the inoculation of 
pure cultures. Colonies of club-shaped organisms 
developed with considerable uniformity. In many 
instances the infection remains localized, not caus- 
ing the progressive and destructive changes which 
actinomycosis produces when it occurs naturally. 

The organism has been found on grains, straws 
and other kinds of feed, with which it may be im- 
planted in the soft parts of the mouth (gums, 



Artificial 
Infection. 



Transmission 
and Infection 
Atria. 



632 INFECTION AND IMMUNITY. 

tongue), or in carious teeth. Transmission to man 
by eating the meat of actinomycotic cattle has not 
been noted. In man the disease is primary in the 
internal organs (lungs, intestines, liver, brain, 
etc.) in a large percentage of the cases, whereas 
"lumpy jaw" is rare. The disease extends locally 
the gradual involvement of adjacent tissues, 
which in time become occupied by sinuses, ab- 
scesses and masses of connective tissue. Numerous 
"spores" and bacillus-like cells, having their source 
in the fungous threads, abound in the vicinity of a 
colony. The occurrence of such forms in leuco- 
cytes and other large mononuclear cells has led 
some to the view that the micro-organisms may 
be carried to neighboring tissues or to distant 
parts as cell inclusions. In cattle the disease usu- 
ally is more chronic than in man, more fibrous tis- 
sue is for. ned and metastases in internal organs 
are less frequent. In man the lesions are more 
purulent in character, large abscesses sometime 3 
form as in the liver, and metastases in visceral or- 
gans are more common. Cases of general acti- 
nomycosis are occasionally met with in both catt-3 
and man. 
Prophylaxis. Little can be said in the way* of prophylaxis 
against actinomycosis. Knowing the part that in- 
fected grains, straws, etc., play in causing infec- 
tion, the practice of biting or chewing grains or 
of using straws as toothpicks, evidently is one 
which affords opportunity for infection. The pres- 
ence of carious teeth has often been suggested as 
a predisposing condition for infection. 
immunity Practically nothing is known concerning the de- 
tiMifty" gree to which susceptibility to actinomycosis pre- 
vails, and the question of immunity to the disease 



MADURA FOOT. 633 

remains unexplored. The inability to reproduce 
the infection in animals at will renders a satisfac- 
tory study of these questions very difficult. The 
presence of large numbers of polymorphonuclear 
leucoc}'tes in the vicinity of the organisms sug- 
gests, but does not prove, that they may have some 
influence in combating the infection. Surely the 
abundant mass of connective tissue which develops 
about the abscesses and sinuses aids in confining 
" the process to a definite region. 

That the iodid of potassium has a curative influ- 
ence on some cases of actinomycosis seems to have 
been well demonstrated. The principles by which 
it produces its effects are unknown. 

VI. MADURA FOOT. 

Mycetoma, or Madura foot, resembles actinomy- Mycetoma. 
cosis in the formation of abscesses, sinuses and 
granulation tissue, but it shows a peculiar predilec- 
tion for the foot, which probably is explained by 
the greater exposure of this part to infection. This 
disease differs from actinomycosis in that the 
course is more chronic and it is never accompanied 
by generalized infection. The bones are not in- 
volved so frequently as in actinomycosis. Granules 
similar to those of actinomycosis are found in the 
cells, which, however, do not assume the pro- 
nounced club shape seen in colonies of the ray fun- 
gus. 

Two varieties of the disease are known, one in 
which the granules are brown or black, and an- 
other in which they are white or yellowish; the 
. latter is encountered much more frequently than 
the former. 






034 INFECTION AND IMMUNITY. 

Pure cultures of the organism, which is callel 
Streptothrix madurce (Vincent), were first ob- 
tained by Vincent in 1894, and have been studied 
by a number of observers since that time. It bears 
a close resemblance to the actinomyccs and by some 
msidered a variety of this organism. Differ- 
ences between the black and white varieties are not 
clearly set forth. The disease occurs in southern 
Asiatic countries, in northern Africa, and in the 
United States (rare). 

TIL INFECTIONS BY STREPTOTHRIX, CLADOTIIRIX 
AXD LEPTOTHRIX. 

streptothrix Cultures of streptothrix, differing from the 
actinomyces, have been obtained from the lungs 
in a number of instances and in various countries. 
They have been found in such lesions as broncho- 
pneumonia, or more extensive consolidation of the 
lungs, and in cases of empyema. In other instances 
organisms which have been classed, some as strep- 
tothrix, others as cladothrix, have been cultivated 
from processes which resembled actinomycosis. 

Xocard considers a streptothrix as the cause of 
farcin du bceuf (farcy of cattle), a disease encoun- 
tered especially in the countries of southern Eu- 
rope, and similar organisms have been cultivated 
from suppurating or granulomatous foci in other 
animals. 

Leptothrix buccalis, a thread-like organism 
which does not form branches and, hence, is not an 
actinomyces nor a streptothrix, is frequently found 
as a saprophitic organism in the mouth cavity, and 
a similar fungus, Leptothrix vaginalis, has been 
encountered in the vagina. Although organisms 
of this type are relatively harmless, they have occa- 



OIDIOMYCOSIS. 



G35 



sionally been found in diseased conditions of the 
tonsils and pharynx. 



Oidiomycosis. 



VIII. OIDIOMYCOSIS. 

In 1894 Gilchrist described a skin disease, which "Biastomy- 
has since been known as blastomycetic dermatitis, matitis. er ~ 

or blastomycosis or oidiomycosis of the skin. From 
a second case he cultivated a fungus which at first 
he was inclined to consider as an oidium, but later 
called a blastomyces. Since that time many simi- 
lar cases, especially in Chicago and the adjacent 
territory, have been discovered and reported by 
Wells, Hektoen, Hyde and Montgomery, Bicketts 
and others. In many instances the specific fungi 
have been cultivated. 

Further investigations by Eixford and Gilchrist, systemic 
Busse, Curtis, Hyde and Montgomery and others 
have brought to light the existence of systemic 
infections by fungi which are identical with those 
found in blastomycetic , dermatitis, and cases in 
which the disease primarily was limited to the 
skin have gone on to generalized infection. The 
converse is also true, that infections which pri- 
marily are systemic, or rather pulmonary, give rise 
to secondary invasion of the skin in a large per- 
centage of the cases. Busse and Curtis both de- 
scribed infections with these organisms as Sac- 
char omyco sis liominis, on account of the fermenta- 
tive powers of the organisms concerned. Sacclia- 
romycosis liominis, blastomycetic dermatitis and 
generalized blastomycosis are identical processes 
pathologically which have as their cause a group of 
fungi, the individual strains of which may show 
considerable differences. A similar disease which 






636 INFECTION AND IMMUNITY. 

has been observed in South American States and 
in California was formerly considered as a proto- 
zoic infection, but Ophiils and Moffitt have shown 
that this disease also is caused by a fungus which 
has many points of similarity with the organisms 
of local and systemic blastomycosis. 

The number of observed cases of systemic blas- 
tomycosis has increased greatly of late. Twenty- 
four have been reported. . and of these 18 or 
19 are known to have proved fatal; three appear 
to have recovered spontaneously or under treat- 
ment, especially with potassium iodid or cop- 
per sulphate (Bevan). That the disease has often 
been passed over for systemic tuberculosis seems 
very probable (one such case is known), and that 
ii is much more common than usually supposed is 
indicated by the recognition of five cases in the 
wards of the Cook County Hospital (Chicago) by 
Stober and others from June until January of 
1907. 
Nature of In blastomycetic dermatitis and systemic blas- 
tonrycosis, the fungi proliferate in the tissue by 
budding, and arc found chiefly in the intra-epi- 
thelial and subcutaneous abscesses, and in the 
granulation tissue, nodules and abscesses of inter- 
nal organs. Their appearance in culture media 
and their biologic properties are subject to consid- 
erable variations, at one time growing as a mold, 
at another time more like the typical oidium, and 
again resembling some form of } T east. Eicketts 
considers that the genus oidium is sufficiently 
broad to include all the types which have been 
described, and that the term blastomyces is too 
narrow. He applies the name of Oidiomycosis to 



Fniifti. 






PATHOLOGY OF BLASTOMYCOSIS. 637 

the disease. The organisms which have been cul- 
tivated from the cases in California grow as molds, 
and they differ from those described by Gilchrist, 
Hektoen, Eicketts and others in that they form 
endospores and apparently do not bud in the tis- 
sues of the host (Ophiils, Wolbach). This feature 
is so constant that it would seem to constitute a 
specific difference between these organisms and 
those found in blastomycosis. There are reasons 
for believing, however, that endospore formation 
is a facultative property of at least some of the 
organisms of blastomycosis (LeCount and Myers), 
and if this proves to be true, the two groups are 
brought very close together biologically as well 
as morphologically. Ophuls calls this parasite 
Oidium coccidiodes, agreeing with Eicketts as to 
the generic character of the group, and the cor- 
responding disease bears the name of coccidiodal 
granuloma. 

The skin infection in both diseases usually ap- Pathology. 
pears as a coarse warty and ulcerative lesion, in 
which the large papillae and cutaneous areola are 
beset with minute abscesses; the process extends 
gradually and eventually may involve large areas. 
Microscopically, the tissue shows an enormous epi- 
thelial hyperplasia with intraepithelial abscesses, 
and a richly cellular, granulomatous condition of 
the subepithelial tissue, in which giant cells and 
small abscesses are found. When the disease is 
systemic, various organs, especially the lungs, 
spleen and kidneys, skin and joints, are the seats 
of abscesses and nodules which contain the para- 
sites in immense numbers, and many giant cells 






638 INFECTION AND IMMUNITY. 

of the Langhans type. The lungs show lobular 
or more extensive consolidation. 

The lymph glands show little involvement in 
blastomycosis; it is believed that metastases usu- 
ally take place through the blood stream, which 
may depend on the large size of the organisms. 
On the other hand, there is marked lymphatic 
involvement in coccidioidal granuloma, and it is 
probable that the liberation of minute endospores 
favors lymphatic metastasis. Pathologically, the 
two diseases seem to be differentiated somewhat 
by the fact that coccidioidal granuloma presents 
a greater degree of necrosis and caseation than 
blastomycosis, and the lesions in the former bear 
a closer resemblance to tuberculosis than do those 
of blastomycosis (Hektoen). The differences, 
however, seem to be in degree rather than in kind, 
indicating a certain lack of correspondence in the 
pathogenic properties of the organisms concerned. 
infection The skin infection occasionally follows slight 
traumatism, while in other instances no predispos- 
ing condition is known by the patient. The occur- 
rence of cutaneous lesions in crops has been noted, 
and suggests that in some instances they may orig- 
inate as embolic foci from a pulmonary lesion 
which later heals or becomes latent. In the sys- 
temic infection the primary lesion appears to be 
in the lungs in most cases, from which the blood 
and other organs, including the skin, may be in- 
vaded. Pulmonary oidionrycosis simulates pul- 
monary tuberculosis. In extensive involvement of 
the lungs the organisms may be demonstrated in 
the sputum. 



Atrin. 



THRUSH. 639 

At present, little is known concerning immu- 
nity to these infections. Eicketts prepared a vac- 
cine by disintegrating the organisms in a ball- 
mill, and in collaboration with Eggers found that 
the immunization of animals with the vaccine 
causes the formation of agglutinating or precipi- 
tating antibodies (from unpublished experiments) . 
The practical value of the vaccine has not had a 
thorough trial. Christensen and Hektoen used 
it in two cases of systemic blastomycosis which, 
however, were so far advanced that no conclusions 
as to the value of the treatment could be drawn. 
Theoretically, the conditions would seem to be 
favorable for the vaccine treatment of blastomy- 
cosis, since the disease is of a chronic character 
and there is little opportunity for autoimmuniza- 
tion on account of the dense capsule which sur- 
rounds the organisms. By grinding the organ- 
isms up, their constituents may ■ be injected in 
such condition that they are readily absorbed. 

Thrush. 

Ophtils very properly suggests that thrush 
should be considered as one form of oidiomycosis. 
Thrush is of particular interest because of the early 
date at which its parasitic nature was recognized. 
Langenbeck and Berg, in 1839 and 1841, are cited 
as the discoverers of the fungus, and they repro- 
duced the disease by inoculations with fragments 
of the membrane. The parasite was studied a little 
later by Gruby, Eobin and others, and the latter 
gave it the name of Oidium albicans. Grawitz ob- 
tained it in pure culture in 1877 and demonstrated 
its pathogenicity for dogs and rabbits. 



640 INFECTION AND IMMUNITY. 

Cultures of the organism show differences in 

size, morphology, chemical activities and methods 

of proliferation, although the variations are hardly 

so wide as those found among the fungi cultivated 

systemic from cases of "blastomycosis." 

infection. Although thrush usually is considered a rather 
harmless affection, Virchow long ago showed that 
its filaments may penetrate the submucous tissues 
and even the lumens of blood vessels. In rare in- 
stances systemic infection, with abscesses in the 
brain, kidney and spleen or with nodules in the 
lungs, has been noted; in these cases the condi- 
tions resemble those found in systemic "blastomy- 
cosis." 

The healthy person has little or no susceptibility 
to thrush, although a few cases of infection have 
been noted in individuals who were otherwise nor- 
mal. Customarily it attacks only those who are 
in a low state of vitality, as poorly nourished chil- 
dren or those in advanced age, or those whose re- 
sistance is much lowered by some other disease (ty- 
Phagocytosis phoid, diabetes, etc.). 
and Im ™ t u- Phagocytosis of yeast and oidium-like cells takes 
place when they are placed in the abdominal cav- 
ity of experiment animals (guinea-pigs). A num- 
ber of leucocytes may fuse to form a plasmodial 
mass around one or more of the parasitic cells. 
Eoger and Noisette caused an increase in the re- 
sistance of rabbits to thrush infection by the intra- 
venous injection of small doses of the parasite. Ac- 
cording to Noisette, an immune serum agglutinates 
only the strain used in the immunization. 

Infections of other animals (horses, cattle) by 
oidium-like organisms, the trichophyton and other 
fungi which cause superficial diseases in the skin 



ASPERGILLUS. 641 

of man, and other fungi (aspergillus, mucor), 
which occasionally are pathogenic for man, will not 
be discussed. 



CHAPTEE XXVIII 
GROUP V. 



DISEASES DUE TO SPIBILLA. 



I. RELAPSING FEVKU. 



The organ- In 1868, Obermeier discovered in the blood of 
patients suffering from relapsing fever, "Very fine 
threads exhibiting motility." These "threads" 
have since been known as the Spirillum obermeieri 1 
and are recognized as the cause of the disease. 
Xovy describes two forms of the organism. The 
short forms vary from 7 to 9 microns, and are 
about 0.25 microns in width. The long forms vary 
from 16 to 19 microns. They result from processes 
of agglutination or multiplication. The organism 
is provided at one end with a long flagellum. The 
turns of the spirals of the short forms are two or 
three in number. The spirilla are very motile, 
and not only move from place to place but rotate 
on the long axis. 

1. The spirillacse, Migula's third family under the 
Order of Eubacteria, comprises organisms with these char- 
acteristics : "Cells which are twisted screw-fashion or repre- 
sent a segment of a spiral. Division takes place only in one 
direction of space after the cell has elongated." The dif- 
ference between spirillum and spirocha^ta is shown by the 
following : "3. Genus : Spirillum. Cells rigid, with polar 
tufts, for the most part bent in the form of a half-circle, 
as organs of locomotion. 4. Genus : Spirochsta. Cells with 
snake^like bending, organs of locomotion unknown." 
Although Migula classes this organism with the bacteria, 
there is some ground for considering it protozoon in nature. 
According to Novy, the organism of relapsing fever has a 
rigid cell body with an end flagellum and would therefore be 
be classed as a spirillum. 



RELAPSING FEVER. 643 

The organism has not been grown artificially, 
but it may be kept alive for a number of days in 
the blood or serum of patients. As the micro-or- 
ganisms die, agglomerations are formed and they 
undergo granular changes. 

The organism is not found in Nature, and, 
since it occurs only in the blood of the sick, it has 
long been assumed that infection can be accom- 
plished only by the inoculation of infected blood. 
The parasites have been demonstrated repeatedly 
in bedbugs which are found on the mattresses of 
the sickbed, and monkeys have been infected by 
inoculating them with the blood found in the 
bodies of these insects, and by the bites of the lat- 
ter (Tictin). It is said that they may remain 
alive in bedbugs for as long as thirty days. It is 
not altogether excluded that other vermin also 
transmit the disease. 

The spirochete does not appear in any of the ex- 
cretions, unless these happen to be of a bloody 
character. 

Certain monkeys, those belonging to the slender- 
nosed family (Catarrhince), may be infected by 
injecting the blood of patients, provided the blood 
used is taken during the paroxysm, i. e., at a time 
when the microbes are known to be in the blood. 
Novy has found that the disease can be readily 
transmitted to white rats and mice; rabbits and 
guinea-pigs appear to be refractory. In mice, as 
in monkeys and man, relapses occur regularly. 
In rats, however, immunity is established after 
one attack. The incubation period in man usually 
is from five to seven days, and in monkeys from 
one and one-half to four days. Cloudy swelling 



G44 IXFECTIOX AND IMMUNITY. 

of the parenchymatous organs, ecchymoses and 
infarcts of the spleen and kidneys are found in 
fatal cases. 

Prophylaxis consists in isolation of the patient, 
cleanliness, and the destruction of vermin, espe- 
cially bedbugs. 

Kelapsing fever occurs in various races of man, 
and so far as known none is immune. 
immunity. Ag gtated ^^ & remarkable feature in the 

course of the disease is the rapidity with which the 
micro-organisms disappear from the blood at the 
time of the crisis. Metchnikoff refers this to 
phagocytosis by the microphages, which undergo 
a progressive increase during the paroxysm and 
decrease after the crisis. Very little phagocytosis 
appears to take place in the circulating blood, but 
in the spleen many spirochetes are found within 
polymorphonuclear leucocytes. 

Tictin also found the spirochetes in the paren- 
chymatous cells of the kidney, liver and lungs. 
Phagocytosis is most marked at or near the time 
of the crisis. According to Metchnikoff, relapse 
or reinfection is accomplished by spirochsetae which 
again invade the body from the spleen. 

According to Novy and Knapp, two distinct 
types of: protecting substances develop during the 
course of the disease. They describe a germicidal 
substance which causes bacteriolysis both in vitro 
and as observed in Pfeiffer's phenomenon. In ad- 
dition to this germicidal substance, they believe 
that a second protecting substance, which they 
term the immune body, is present. The existence 



THEORY OF RELAPSES. 645 

of the immune body is established by the fact that 
passive immunization can be accomplished by the 
use of serum having no germicidal action. Phago- 
cytosis is concerned chiefly with organisms killed 
by the germicidal agent. Marked agglutination 
occurs with immune serum. 

The immunity conferred by an attack of relaps- 
ing fever is probably of long duration. Other ani- 
mals are also immune to a second infection. 

The development of immune bodies which oc- Theory of 
curs with the first febrile period is insufficient to 
cause complete destruction of the spirilla. A few 
of these, aided possibly by their sheltered location 
in lymph spaces, survive and may become immu- 
nized to some extent against the antibodies. These 
organisms by multiplication institute a second 
febrile period which is followed by a higher devel- 
opment of immune bodies. Each relapse has the 
effect of heightening the immunization until com- 
plete destruction of the organisms occur. 

Hereditary immunity may result from intra- Hereditary 
uterine infection. Spirilla have been found in 
the heart's blood of the human fetus. Novy and 
Knapp describe the occurrence of both active 
hereditary immunity occurring in the young of 
infected rats and passive hereditary immunity oc- 
curring in the young of rats passively immunized. 

It is evident from the work of Novy and Knapp 
that the chief difficulty in the production of a 
curative serum is that of the cultivation of the 
spirillum. It may be possible, however, to immu- 
nize larger animals with infected blood and thus 
obtain an efficient antiserum. 



Immunity. 



646 INFECTION AND IMMUNITY. 

In addition to the European relapsing fever 
there are at least three recurrent fevers caused by 
varieties of spirilla distinct from one another in 
morphology and according to Kolle and Schatiloff 
in complement deviation. One of these three 
forms occurs in India. The other two are known 
as African tick fever. Of these two forms, that 
of West Africa was studied by Dutton and Todd. 
The other form is prevalent in East Africa and 
was studied by R. Koch. According to Koch, the 
ticks which carry the organisms also transmit 
them to the eggs, which in turn develop into ticks 
capable of infecting man. Koch found spirilla in 
only a part of the eggs of infected ticks. 

II. SYPHILIS. 

Historical ]t is impossible here to describe or even men- 
Data. 1 

tion the many cocci, bacteria and protozoa (?) 

which have been brought into etiologic relation- 
ship with syphilis. Until recently, the bacillus of 
Lustgarten occupied a fairly prominent position 
as the possible cause. This organism resembles 
the tubercle bacillus in its morphology and stain- 
ing properties, and is not to be differentiated from 
one of the smegma bacilli. Its recognition in 
syphilitic lesions has always been difficult, and by 
far the greatest number of investigators have been 
unable to demonstrate it. It has never received 
general recognition as the cause of the disease, and 
its presence in lesions of the genitals has no sig- 
nificance because of the occurrence of smegma bac- 
illi in this locality. 

The bacillus of De Lisle and Julien, and that 
of Joseph and Piorkowski rest on no better basis. 



SYPHILIS. 647 

In 1905, Hoffman and Schaudinn discovered in Spirociia-ta 
the primary and secondary lesions of syphilis, a 
very delicate spirochete which they named Spiro- 
chceta pallida on account of the difficulty of stain- 
ing it with anilin dyes. 

The spirillum is of corkscrew-like form with 
from six to thirty turns. It is about V^ micron in 
thickness, and from 4 to 26 microns in length. 
The turns are regular and deep in the middle and 
become less pronounced toward the ends. There 
is a fine nagellum at each end of the spirillum. 
When observed in serum by means of dark-field 
illumination, the organism exhibits marked motil- 
ity. Movement may be observed both forward and 
backward; rotary and bending motion is also seen. 
Stained with Giemsa's eosinate of azur, the spirilla 
are stained a pale rose color. According to Schau- 
dinn, division takes place longitudinally, and in 
this respect the spirochete resembles the trypan- 
osomas. The systematic position of the organism- 
is not yet certain. Cultivation has been reported 
by a number of workers. The cultures were not 
pure, however, and the spirochetes were non-viru- 
lent. 

The Spirochceta pallida has been found in the 
lesions of all stages of syphilis. These organisms 
are found in great abundance in the primary les- 
ion and in the tissues of the infected regional 
lymph glands. They are easily detected in the 
tissues affected in secondary syphilis. Although 
found in the circulating blood, they occur only 
occasionally or in small numbers. In the organs 
affected by fetal syphilis, spirochetes are found in 



Anatomic 
Distribution. 



G4S 



J.XFECTIOy AJD IMMUNITY. 






Experiments 

of Metchnikoff 

anil Itonx. 



I r:iiiMiiis>iini 

from Monkey 

to Monkey. 



great abundance. In tertiary syphilis the lesions 
contain only a few organisms. Those present are 
most numerous in the tissues surrounding the 
necrotic center. 

It occurred to Metchnikoff and Eoux as it had 
occurred to others that the monkey, particularly 
the higher species (chimpanzees), should on ac- 
count of their biologic proximity to man, be the 
most suitable animal for the production of experi- 
mental syphilis. Attention has already been called 
to this proximity as indicated by the reaction of 
serum precipitins. 

Their first inoculation was performed on a fe- 
male chimpanzee, virus from a primary lesion and 
from mucous patches being intr6duced by means 
of scarification into the prepuce of the clitoris and 
into the skin of the eyebrow. The wounds healed, 
and twenty-six days after inoculation a vesicle 
which soon was surrounded by induration appeared 
on the prepuce. This lesion was pronounced a typi- 
cal hard chancre by eminent dermatologists and 
syphilologists. With the appearance of the chan- 
cre the inguinal lymph glands became enlarged, 
and one month later a papular eruption appeared 
on the thighs, abdomen and back. The papules 
persisted for more than a month, and were still 
discernible when the animal died several weeks 
later of pneumococcus infection. Before this ani- 
mal died a second chimpanzee was inoculated from 
the primary and secondary lesions of the first ani- 
mal, resulting in the development of primary le- 
sions and of adenitis. Still another successful in- 
oculation resulted in secondary lesions with the 
formation of mucous plaques. These observers 
have since performed many similar experiments 



SYPHILIS IN ANIMALS. G49 

with positive results, when the higher types of 
monkeys were used. Confirmation has come from 
a number of independent experimenters (e. g., 
Lassar, A. Neisser, Kraus, Flexner), and A. Neis- 
ser in particular has taken up the work on an 
extensive scale. 

Some of Neisser's work is of the utmost impor- Experiments 

Of \^i.SS€M*» 

tance. The experiments of Metchnikoff and Eoux 
had already indicated that the higher monkeys 
(chimpanzee, etc.) acquired generalized syphilis 
more readily than the lower species. Neisser's 
work corroborates this, and he recognizes a scale of 
susceptibility which corresponds roughly with the 
proximity of the different species to mam, as indi- 
cated by general morphology and the reaction of 
serum precipitins. The chimpanzee, orang-utan 
and gorilla are the most susceptible, and the syph- 
ilis produced in them approaches closely that seen 
in man, including the secondary symptoms. It is 
suspected that the cynocephalus varieties are less, 
and the macacus varieties least susceptible. Among 
the macaci the smaller types (rhesus) are more 
resistant than the larger. The lower susceptibility 
of these animals is recognized by the failure of 
secondary symptoms to develop, hence in them the 
syphilis may be purely local (Neisser). Spiro- 
chetes have been found in all the lesions of experi- 
mental syphilis in monkeys. 

Bertarelli first succeeded in producing experi- sypiims 
mental syphilitic keratitis in the rabbit and found AnimaiJ. 
associated with it the Spirochceta pallida. His 
work has been verified by various observers. Muh- 
lens and others have been able to produce a pri- 
mary lesion in the guinea-pig by material taken 
from syphilitic keratitis in the rabbit. 



650 



INFECTION AXD IMMUNITY. 



spirochaeta The fourth postulate of Koch, that of cultiva- 

theCaus* of tion in pure culture and reproduction of the dis- 

s> piniiN. eage ^y means f &uc h p-Qj-g cu itures ? has not yet 

been carried out. The occurrence of the organism 
as described has, however, been such strong evi- 
dence that the Spirochccta pallida is accepted as 
the cause of syphilis. 
infection. Infection usually is venereal. It is not defi- 
nitely known whether a defect of the surface of the 
prepuce, glans, vagina, etc., is essential for infec- 
tion. The epithelium in these localities is so deli- 
cate that defects of microscopic dimensions may be 
easily produced, and infection may take place 
through such defects as through grosser lesions. It 
is well known that the lip, tongue, conjunctiva and 
finger may be the seats of primary lesions, and it 
is probable that no part of the body surface is 
immune when the virus is introduced suitably. 
virnience. Clinical experience indicates that the virulence 
of the Spirochceta pallida is not uniform. It is 
possible that certain strains- are more likely to 
bring about "post-syphilitic" diseases than others. 
That the resistance of the organism outside the 
body is low seems evident from the fact that trans- 
mission is practically unknown except as it occurs 
by direct contact. Neisser destroyed it by heating 
to 60° C. for thirty minutes, but at this tempera- 
ture for ten to twenty minutes its virulence for 
monkeys was retained. 

Prophylaxis demands no principles not generally 
known. 

Susceptibility to syphilis varies a great deal, not 
in the sense that some are immune, but in that a 
more virulent type of disease develops in some than 
in others. This is a condition, however, which 



IMMUNITY IN SYPHILIS. 651 

is difficult to differentiate from variations in the 
virulence of the infecting agent. Syphilis is said 
to be particularly virulent when introduced into 
a race of people for the first time. 

There is no reason to believe that natural im- immunity. 
munity to syphilis exists in man. It was formerly 
believed that the fact that many prostitutes who 
were exposed to syphilis over a considerable length 
of time and who at no time showed active symp- 
toms, were immune to the disease. The rinding 
of positive Wassermann reactions in a large per- 
centage of such individuals would indicate, how- 
ever, that they did acquire syphilis. Through the 
application of the Wassermann test, it has also 
been shown that the laws of Colles and Profeta 
are also incorrect. The former states that the 
mother who gives birth to a syphilitic child with- 
out herself showing signs of the disease, is immune 
to syphilis. Knopfelmacher and Lehndorf ob- 
tained positive Wassermann reactions in 56 per 
cent, of such mothers. Profeta's law states that a 
healthy child, born of a syphilitic mother, can 
suckle the mother without becoming infected. In 
this case many of the so-called healthy children 
have been found to be syphilitic, and others which 
were actually non-syphilitic have been observed to 
contract the disease from the mother. 

Eegarding second infections, experiments on 
apes have shown that second infections are readily 
produced at any time after the primary lesion has 
developed. Such infections are possible even after 
thorough courses of treatment terminating in re- 
covery. These second infections differ from the 
first in that the incubation period is shorter and 



652 INFECTION AND IMMUNITY. 

the course of development and healing of the 
lesion is more rapid. 

Apes with tertiary syphilis react (according to 
Finger) to inoculation with syphilitic material, 
with the formation of tertiary lesions. 

Finger conceives of the process of immunity in 
syphilis as similar to the phenomenon of allergy 
of V. Pirquet. That is in a variation in the capa- 
bility of reaction without the establishment of 
non-susceptibility. Second infections with syphilis 
have also been observed clinically. 
sero reaction The serum reaction is discussed fullv in the 

and Sero- m m J 

therapy, chapter on complement deviation. 

The efficiency which is promised by the recent 
preparation of Ehrlich, known as salversan, leaves 
but little to be desired as a therapeutic agent. The 
lack of production of immunity also renders the 
possibility of a curative serum very doubtful. 

III. FRAMBESIA. 

Frambesia or yaws is a tropical disease found 
in both hemispheres. Castellani found a spirillum 
associated with the lesions which corresponds mor- 
phologically with the Spirochceta pallida. Owing 
to this similarity in the organisms, and to the 
fact that yaws resembles syphilis clinically, the 
two have been considered as different forms of the 
same disease. Castellani, however, finds that in 
the complement deviation reaction neither anti- 
gen nor antibody can be used interchangeably. He 
considers the two spirochetes as distinct from each 
other and names the spirochete of yaws, Spiro- 
chceta pertenuis. Transmission occurs by direct 
contact and probably also by means of flies. 






OTHER SPIROCHETES. 653 

IV. OTHER SPIROCHETES. 

Among other pathogenic spirilla may be men- 
tioned Spirochwta anserina, of the spirillosis of 
geese, Spirochceta gallinarun, causing a fatal dis- 
ease of chickens and 8. Tlieileri, found in a disease 
of cattle in Africa. The last two are transmitted 
bv ticks. 



CHAPTER XXIX. 
GROUP VI. 



PtfOTOZOON INFECTIONS. 
I. MALARIA. 

Etiology. The etiology of malaria, which for long was 
supposed to be associated with impure and swampy 
atmospheres (malaria is from mal' aria, Italian, 
meaning bad air), remained unknown until 1880, 
when Laveran discovered ameboid, half-moon 
shaped and flagellated forms of a parasite in the 
blood of the patients. In following years Golgi, 
Grassi, Marchiafava and Celli and many others 
took prominent parts in working out the different 
forms of parasites, their sexual characters and their 
relation to the different types of malaria. 

Ross and The conception that mosquitoes may be influen- 
tial in transmitting malaria is a very old one and 
its origin is unknown. In 189-1 Manson suggested 
that the malarial organism may utilize the mos- 
quito as an intermediate host where, after under- 
going further development, it again becomes in- 
fectious for man. He was inclined to think that 
the flagella are reproductive forms, which are 
essential for an extra corpus life of the parasite. 
The proof of this came from MacCallum in 1897, 
who showed that the flagellated forms are really 
spermatozoites, the function of which is to im- 
pregnate female cells of the parasite. This was 
observed first in relation to halteridium, one of 



MALARIA. 



655 



the organisms of avian malaria, and later in rela- 
tion to the parasites of human malaria. 

In the same year Eoss found the pigmented, 
half-moon shaped parasites of aBstivo-autumnal 
fever in the stomach of the anopheles mosquito. 
Through the work of Ross and others it is now 
established that the malarial parasite undergoes 
further development, a sexual cycle, in anopheles, 
and that man is inoculated only by the bites of 
such infected insects. From the standpoint of 
the zoologist, man is an intermediate host for the 
parasite, since the latter undergoes its higher de- 
velopment only after it reaches the mosquito. 

The malarial parasites of man belong to the 
class of Sporozoa; order, Coccidiomorpha ; family, 
Hemosporidia ; genus, Plasmodium. The follow- 
ing are the names given to the three species: 1. 
Plasmodium prcecox (parasite of sestivo-autumnal 
fever) ; 2. Plasmodium vivax (of tertian fever) ; 
3. Plasmodium malarice (of quartan fever). 

When the blood of one suffering from tertian 
fever is examined at the end of the febrile parox- 
ysm, or at the beginning of the afebrile stage, the 
parasites are found within the erythrocytes as pale, 
rather clear bodies, about one-fifth the diameter of 
the corpuscle, and in fresh specimens showing an 
active ameboid movement. They are very difficult 
to recognize in unstained specimens. They increase 
in size gradually, and after eighteen hours, when 
they begin to acquire pigment, they are recognized 
more easily. After twenty-four hours the pig- 
ment has increased markedly and the erythrocytes 
are swollen and pale. In stained preparations the 
periphery of the parasite stains more deeply than 
the center and gives it a pronounced ring form. 



Species of 

Plasmodium. 



Tertian 
Fever. 



GoG INFECTION AND IMMUNITY. 

segmentation At the end of thirty-six hours they have increased 
of Asexna^ no ti cea kiy i n s j ze an( j their ameboid motion is 
less. Shortly before the next attack — i. e., from 
forty-six to forty-eight hours after the preceding 
one — the pigment assembles into one or two groups 
in the center of the parasite and clear hyaline 
points begin to appear. These are the young endo- 
cellular parasites which are formed by division of 
the nucleus of the mother cell. They gradually 
increase in size and number, and as the red cor- 
puscles disintegrate they are discharged, from fif- 
teen to twenty-five in number, as young parasites. 
This completes the cycle, an asexual cycle, which 
lias lasted forty-eight hours, and the young forms 
then begin a new cycle after penetrating other red 
corpuscles. The mother cell is called the sporo- 
cyte and its offspring are merozoites, and the proc- 
ess of division schizogony. 
sexnai In addition to the asexual cell just described, 
two sexual cells, a male and a female, grow to 
adult size in the erythrocytes, acquire pigment and 
eventually become free. They differ from the 
asexual cell in that the pigment continues to be 
uniformly distributed, and neither gives rise to 
young parasites by division. The male cell (micro- 
gam etocyte, 8-9 microns) has a clear protoplasm 
and is smaller than the female (macrogamete, 
10-14 microns) ; the female has a granular proto- 
plasm. There are many more male than female 
cells. They undergo no further development in 
the body of man, and in order that the sexual pro- 
cess be completed the two cells must first gain 
entrance into the stomach of the female anopheles 
mosquito. 



MALARIAL PARASITE. 



657 



Impreg- 
nation. 



Life in the 

Mosquito, 



A further step in the sexual process may be seen 
in drop preparations of the blood, although this 
step does not occur in the human body. From ten 
to twenty minutes after such a preparation has 
been made the male cells, after a period of agi- 
tation, discharge from four to eight long, thin 
flagella (microgametes or spermatozoa), which 
thrash about violently and eventually come in con- 
tact with a female cell, which they enter and be- 
come unrecognizable. 

This same process is instituted and completed 
(sporogony) in the stomach of the mosquito, the 
penetration of the female cell by the spermatozoon 
resulting in the impregnation of the former. Fol- 
lowing impregnation, the female cell gradually 
assumes a worm-like or sickle shape (ookinet), 
penetrates the wall of the stomach and becomes 
encapsulated (oocyst). Forty-eight hours after 
the mosquito has sucked malarial blood all the 
female cells have reached this stage and no more 
free parasites are found in the stomach. 

About five days after the blood was taken the Formation of 
oocyst has increased in size about six times and 
has formed within itself a number of small 
spheres, which are called daughter cysts or sporo- 
blasts. The latter soon acquire a finely striated ap- 
pearance, which is due to the formation of hun- 
dreds of "germinal rods" or sickle-like bodies 
(sporozoites). The latter are nothing less than 
young malarial parasites, which are thrown into 
the body cavity by the rupture of the oocyst, and 
are carried to the salivary glands of the mosquito 
by the lymphatic circulation. If the mosquito has 
been kept at a temperature of 24° to 30° C. these 
sickle forms first appear in the salivary gland after 



658 



INFECTION AND IMMUNITY. 



Parasite 

of Quartan 

Fever. 



eight to ten days. Such are the cells which are 
inoculated into man by the bite of the mosquito. 
The changes which they undergo before they ap- 
pear as clear oval bodies in the erythrocytes are 
unknown. 

The asexual cycle of the quartan parasite is 
identical with that of the tertian, with the excep- 
tion that seventy-two hours are required for its 
completion. It contains more pigment, and when 
division takes place eight, or at most fourteen, 
young parasites are formed, in contrast to the 
fifteen to twenty-five of the tertian parasites. The 
erythrocytes do not become large and pale (Ruge). 
The sexual cells practically are indistinguishable 
from those of the tertian parasite, although they 
are, on the whole, slightly smaller. The sexual 
cycle also is completed only in the body of the 
female anopheles mosquito, and is identical with 
that of the tertian parasite. 

The parasite of aestivo-autumnal fever is from 
Autumnal one-half to two-thirds the size of the tertian para- 
site, a difference which is constant in the various 
stages of development of the asexual cell. It 
divides eventually into from eight to twenty-five 
young parasites, the cycle occupying from twenty- 
four to forty-eight hours. 

Here, as in quartan fever, the erythrocytes do 
not become swollen and pale, but even appear 
darker in color, because of some shrinking (Ruge). 
The sexual cells in sestivo-autumnal fever are 
characteristic. Whereas they at first do not differ 
in shape from the asexual cells, as the}*- grow older 
they gradually assume the shape of a half moon in 
one edge of the erythrocyte, reaching a length 
equal to one and one-half diameters of the red cell. 



Parasite of 
Estivo- 



"Half-Moon" 
Cells. 



MALARIAL PARASITE. 659 

At this time a fine line drawn across the concavity 
of the parasite represents the margin of the ery- 
throcyte. This form is only temporary, however; 
they subsequently assume first a spindle and then 
a spherical form. ' As in the other parasites, the 
male cell is rather clear and the female granular. 
When mounted in a hanging drop the male cell 
liberates flagella, which penetrate the female cell. 
This does not occur in the human body. In this 
respect, and also in the completion of the sexual 
cycle in the body of the mosquito, they resemble the 
other two parasites. 

The parasites of tertian and quartan fevers un- 
dergo division while they are in the circulating 
blood, and when peripheral blood is examined at the 
end of the afebrile stage the young cells may be 
found extracellular. This is not the case, how- 
ever, in the 3estivo-autumnal fever. In this in- 
stance, for unknown reasons, the adult cells with- 
draw to the internal organs, especially the spleen, 
bone-marrow and brain, where division takes place 
in the minute vessels. Hence if the peripheral 
blood is examined preceding and during the febrile 
stage few or no dividing cells or young parasites 
are seen. 

Following inoculation by an infected mosquito, incubatio 
ten to twelve days are required for the onset of a Period - 
paroxysm. In rare instances the incubation period 
may be as short as five to six days. This probably 
depends to some extent on the number of organisms 
inoculated. Malarial infection of the mosquito 
is not transmitted to the offspring the latter, 1 
hence the bites of young mosquitos do not convey 

1. This is questioned by Schaudinn. 



6G0 INFECTION AND IMMUNITY. 

the disease unless they also have sucked malarial 
blood. The conditions are different in relation 
to Texas fever, in which the infection is trans- 
mitted by the female tick to her young. 

The aestivo-autumnal parasite apparently is 
more virulent than the tertian or quartan. Not 
all cases of tertian or quartan fever are equally 
severe, and these variations may depend on differ- 
ences both in virulence and in the resistance of in- 
dividuals. When all the parasites divide within a 
period of from two to four hours, the paroxysm is 
more intense but shorter than when division ex- 
tends for from six to eight hours (Huge in rela- 
tion to tertian fever). Some of the severer symp- 
toms are due to the localization of the parasites 
(brain and intestines), rather than to special tox- 
icity. 
Relation of The melanemia of malarial fevers is due to the 
the Biology fact that the parasites absorb the hemoglobin from 
Parasites! the erythrocytes, transform it into melanin by 
their metabolic activities and liberate the melanin 
at the time of cell division. The anemia results 
from destruction of the erythrocytes. 

The cause of the fever and its periodic recur- 
rence is more difficult to explain. As stated above, 
the fever begins in both tertian and quartan fevers 
at the time division forms of the parasites are en- 
countered in the peripheral blood. Although all 
the parasites do not divide simultaneously, the 
process is complete within a period of four to 
eight hours and the paroxysm begins early in this 
period. It is quite natural, then, to infer that by 
the division of the parasite and the escape of the 
Fever and y omi S ce ^ s fro m the erythrocytes, toxic substances 
schizogony. are thrown into the circulation, and that the febrile 



MALARIAL PARASITE. 661 

reaction is due to the action of these toxins. 
Methylene blue has the power of preventing seg- 
mentation of the parasites (Ehrlich), and it has 
been shown that the paroxysm of fever may be 
averted by administering methylene blue at the 
proper time. This corroborates the view that the 
segmentation of the parasites causes fever in some 
way. The paroxysm would seem to represent the 
time required for the exhaustion of the toxins set 
free at the time of the cell division. 2 

On the basis of the conditions just cited, the Duration of 
brief duration, sharp limitation and regular re- 
currence of the paroxysms in tertian and quartan 
fevers become intelligible. In a similar manner 
the longer paroxysms and shorter intermissions 
which characterize the typical aestivo-autumnal in- 
fection (i. e., in first attacks) are related to the 
habits of division of the corresponding parasite. 
All the cells do not divide within a relatively short 
period, as in tertian and quartan fevers, but the 
process of division rather stretches out over from 
twenty-four to forty-eight hours. This accounts 
for the longer duration of the paroxysm. When 
the last cells of one generation are dividing, per- 
haps after the fever has gone down, the first cells 
of the succeeding generation are well on toward 
maturity and their division within a short time 
inaugurates a new paroxysm; the brief intermis- 
sion would seem to be explained by this condition. 
As the disease lasts longer, or as relapses develop, 
the periods of division of the parasite are less 

2. Rosenau, Parker, Francis and Beyer produced a typical 
paroxysm in a healthy person by injecting filtered serum 
taken from a tertian patient during the chill This was 
intoxication, not infection 



M iNFMCTIOH A\D IMiirXITY. 

sharply limited an . r» with an irregularly 

DontmiMHifi : :;ver may be established. 
Qu °Fe d ver n rased either by 

a double or a 

triple in: In either 

_ iteration of parasites matures and 
div: /:y-four hours. The cause of 

::on is not known de: 
[n s - - - t s - 

inoculati: s occurred. 

On the other hand ich is primari. 

tian or quartan may gradually change into the 
quotidian it is pos- 

- - 
3 or three _ 

h maturity on si 
x,a j n xheT :r.» ixed inff two 

Infeoiion* 

kin.:- - is usually 

Tumnal fever combined : :- 

tian or with quartan. Either the a?stivo-autumnal 
may be primary on the one hand or the tertian or 
quartan on the other. The clinical course is com- 
plicated corresponding v. It is doubtful if tertian 
with quartan. Euge speaks 
of experiments by Pr. Mattel which indicate that 
a mixed infection does not continue indefinitely 
u r A patient suffering from quartan 

; : be : -autumnal blood; in 

time all the quartan psnsiteE .^appeared, leav- 
ing L. :ii£ ^5::- ;-;..::\:~ ::;... 

In malarial cachexia there is not only an in- 
x>d-forming organs, but 
; ^nchymato"s Digane b*?e suffered as a result 
of prolong . The blood-forming or- 



BLACK-WATER FEVER 



663 



Cerebral and 
Intestinal 

Symptoms. 



gans can not keep pace with the destruction of the 
erythrocytes. 

Trigeminal and supraorbital neuralgias and 
periodic headaches occur sometimes as accompani- 
ments of malarial infection, even when there is 
little or no fever, and no parasites may be dis- 
coverable in the blood. That they are malarial in 
origin is concluded from the fact that they subside 
under quinin treatment. In some forms, and par- 
ticularly in asstivo-autumnal fever, cerebral symp- 
toms (e. g., coma) are marked by accumulations 
of the parasites in the small vessels of the brain; 
the vessels may be completely occluded. The con- 
ditions are similar in the small vessels of the intes- 
tines in malarial diarrheas. 

The so-called "black-water fever," or hemo- "Biack-water 
globinuric fever, is not a special form of malaria, 
but a complication which, it is thought, is pre- 
cipitated by insufficient or improper administra- 
tion of quinin (Koch and others). It is most fre- 
quent in the tropics, hence in sestivo-autumnal 
fever, but may occur in the tertian and quartan 
types. Various observers 'have found that in from 
56 per cent, to 97 per cent, of the cases quinin 
precipitated attacks. Stephens and Christopher 
were not able to exclude quinin as a factor in any 
of the cases they encountered. The essential proc- 
ess is a massive destruction of the erythrocytes 
which is entirely out of proportion to the number 
of cells occupied by parasites; few or no parasites 
may be present. The amount of hemoglobin thus 
liberated is so great that it is excreted largely by 
the kidneys; anuria may result from occlusion of 
the tubules by pigment. How the quinin, or the 
quinin plus parasites, produce this extensive hemo- 



664 INFECTION AND IMMUNITY. 

lysis is entirely obscure; the effect is that of an 
intense intoxication, in which the erythrocytes 
suffer primarily and chiefly. Craig warns against 
the administration of one large dose of quinin in 
the 24 hours in aestivo-autumnal fever lest perni- 
cious symptoms develop. 
Epidemi- The essential epidemiologic features of malaria 
' 0e>> ' are the following: It prevails especially in tropical 
and subtropical zones and less in temperate zones. 
It is most abundant in low, swampy regions, and 
in other places which afford quiet streams, ponds 
or other standing water. It is not directly conta- 
gious. In order to become infected it is necessary, 
customarily, to enter or be in close proximity to a 
"malarial district." That the virus is not carried 
far from an infected district is shown by the 
exemption of crews of vessels which lie within two 
or three miles of such a district. Infection has 
long been supposed to take place chiefly by night. 
The disease may be introduced into new regions 
(of suitable climate) by the importation of mala- 
rial subjects. These and other phenomena of mala- 
ria which were once very obscure have been cleared 
Anopheles, up by the mosquito theory. There are many spe- 
cies of anopheles and they are distributed through- 
out the world in warm and moderate climates. 
Anopheles maculipennis is the most numerous spe- 
cies, and for it, as well as for Anopheles puncti- 
pennis, Howard has found several natural breeding 
places in this country. It is probable that many, 
but not all, species of anopheles may transmit 
malaria. The female only is a blood-sucker, the 
male living on vegetable 'material exclusively. 
After the female has obtained blood from man or 



TRANSMISSION. 665 

another mammal it flies to a suitable pond or other 
collection of water, where it deposits its eggs. 

"The adult mosquito lays its eggs on the surface Development. 
of the water. The eggs float on the water for 
some days (two to four), after which they hatch 
and permit the escape of the larva. 

"The larva is a free-swimming, worm-like ani- 
mal, which eats greedily and grows rapidly, cast- 
ing its skin several times in the process, till it 
reaches its full development. At this stage it sud- 
denly changes its form ; casting its skin, the worm- 
like larva assumes a comma shape and so becomes 
the pupa or nympha. 

"During the pupal period the insect ceases to 
eat; profound anatomical changes take place with- 
in the pupal skin, whereby the masticatory mouth- 
parts of the larva are converted into the suctorial 
apparatus of the adult insect or imago. After a 
certain number of days the pupa case ruptures and 
the adult insect is liberated, furnished with wings 
and legs adapted for a life in the air." (James 
andListon.) 

In one instance Howard found the life cycle of 
Anopheles maculipennis to be: "Egg stage, three 
days; larval stage, sixteen days; pupal stage, five 
days, making a total period in the early stages of 
twenty-four days." The rapidity with which this 
process takes place depends largely on the tem- 
perature; it is more rapid in the hot weather of 
July and August than in the cold days of May. 
Anopheles usually does not lay its eggs in tin cans 
or barrels of water, but preferably in more open 
or cleaner water. Excavations which have become 
filled with water are favorable places, as are also 
collections of water from springs. 



66G INFECTION AND IMMUNITY. 

Migration of The anopheles leads an adult life for many 
months and may even hibernate under suitable 
conditions either in the adult or larval form. It 
is generally stated that the insects do not fly more 
than half a mile from their breeding and feeding 
grounds. Their dispersal certainly extends beyond 
these limits, however. James and Liston enumer- 
ate the following methods of dispersal: (1) by 
direct flight over considerable distances; (2) by 
the eggs and larvae being carried in streams and 
canals; (3) by a multiplication of successive short 
flights by adults; (4) in conveyances. 

Anopheles avoids high winds and rains, seeks 
shelter on excessively hot days and feeds and bites 
chiefly or only after sunset and before sunrise. 
The latter habit confirms the old belief that ma- 
larial infection occurs chiefly at night. 

For further details as to the morphology and 
habits of the insect in its different stages, and for 
differentiation of the different genera and spe- 
cies, one should consult a textbook of entomology, 
or, for example, the book on "Mosquitos," by How- 
ard (McClure, Phillips & Co., New York). 

Prophylaxis. Individual prophylaxis may be accomplished and 
maintained by taking small daily doses of quinin, 
or larger doses (1 gram) every few days. One who 
has had malaria may likewise prevent recurrence 
by suitable quinin treatment. Quinin has the 
power of preventing division of the parasites, and 
therefore, the power of preventing the paroxysms. 
"K. Koch's procedure consists in this, that one 
takes a gram of quinin every tenth and eleventh 
day, and if fever still develops, every ninth and 
tenth day." (Kuge.) 



PROPHYLAXIS. 667 

Other points in individual prophylaxis are, first, 
the application of ethereal oils (clove oil, oil of 
pennyroyal) to the exposed skin, and, second, the 
use of mosquito netting. 

The important practices for general prophylaxis Measures 
are the following: 1. The draining of swampy 
places and of pools of water where anopheles may 
deposit its eggs. This in many instances manifest- 
ly can not be accomplished. 2. Covering pools of 
water with petroleum. This is to a degree success- 
ful. Every square meter requires 0.5 liter of pe- 
troleum (Kerschbaumer), and the oil must be 
added fresh every seven or eight days. The layer 
of oil excludes the air from the larval mosquitoes 
and they drown. If fresh oil is not added occa- 
sionally new eggs may hatch. 3. Koch's method of 
extermination of malaria. This consists of the 
searching out of all cases of malaria and the de- 
struction of the parasites by appropriate quinin 
treatment. Koch practiced this method in an in- 
fected locality of New Guinea and in a relatively 
short time freed it of malaria. If all the plasmodia 
in a community are destroyed the disease can not 
again become endemic unless it is introduced from 
without or unless infected mosquitoes are imported. 
Manifestly this method must be practiced on an ex- 
tensive scale in order to render it permanently 
successful. It seems to have been demonstrated, 
however, that the number of cases in any given 
locality may be materially decreased by pursu- 
ing it. 

So far as is known, susceptibility to malaria is immunity. 
universal. The belief is very general that one 
attack of malaria not only does not protect against 
reinfection, but even predisposes to it. Two facts. 



GGS INFECTION AXD IMMUNITY. 

however, show that acquired immunity (relative 
or absolute) is possible. First, iu certain regions 
of Africa where malaria is endemic the adult na- 
tives rarely suffer from the disease, and then only 
from light attacks, whereas European visitors con- 
tract the disease in severe form. The cause of this 
immunity was explained by Koch. "Koch found 
that the native adults of malarial countries were 
free from malaria, but that the children suffered 
almost universally from malarial diseases. If 
they recovered from the original infection they 
became immunized in time through continued new 
attacks or relapses, the number of malarial chil- 
dren gradually decreased with their age, and in the 
vicinity of the tenth year the only evidence, in 
general, of a previous infection was an enlarged 
spleen, and even this disappeared during puberty, 
so that the adult natives finally appeared as 
healthy and malaria-immune persons." (Huge.) 
The objection raised by many that such immunity 
is not observed in Italy and other civilized coun- 
tries where malaria is endemic, is met by the fact 
that the disease in these countries is not permitted 
to run an uninterrupted course. Treatment with 
quinin is instituted and the immunizing process 
is thereby broken off. Koch also established the 
fact that immunity against one type of parasite is 
not efficient against other types. 

Second, in civilized countries it has often been 
noted that subsequent attacks are of a milder char- 
acter than the primary; the disease may in time 
"wear itself out," even without quinin treatment. 
Euge gives as an accompaniment of this immuniz- 
ing process the occurrence of the sexual cells in 
large numbers, even up to 50 per cent, of the total 



MALARIA OF BIRDS. 669 

number of parasites (tertian fever). In such 
cases large numbers of the parasites die before 
they reach maturity, their death being indicated 
by shrinking and clouding of the cells and altera- 
tions in or disappearance of the chromatin. It is 
somewhat characteristic of quartan fever, and still 
more so of sestivo-autumnal, that the sexual cells 
are much more numerous in recurrences than in 
primary attacks. One may be able to differentiate 
a relapse from the j)rimary attack by the number 
of sexual cells encountered (Huge). 

Nothing in the way of serotherapy has been 
accomplished, and it is doubtful if any serum 
could equal quinin in efficacy. 

MALARIA OF BIRDS. 

Diseases considered to be true malaria also occur in 
birds. 

One of these diseases is caused by a proteosome (Pro- 
teosoma Labbe, Cystosporon danielewshy, Hemameba re- 
lict a). Sparrows, hawks, buzzards, crows and pigeons 
are affected. Like the malarial parasites in man, the 
parasite enters the erythrocytes and has both a sexual 
and an asexual cycle of development, the latter taking 
place in the infected animal, the former in the stomach 
of the common mosquito (Culex pipiens) . Hence in its 
development proteosoma is perfectly analogous to 
Plasmodium. This disease is transmissible from bird to 
bird by the inoculation of infected blood. 

Halteridium is still another hemosporidium which in- 
fects birds. It was in the study of this organism that 
MacCallum first saw the phenomenon of impregnation. 
All the cells seen in the blood appear to be divisible into 
male and female, and although MacCallum had seen im- 
pregnation in microscopic preparations the life cycle for 
a long time was obscure. Recently Schaudinn has found 
that the sexual cycle is completed in Culex pipiens. He 
considers the organism to be a trypanosome. "I have 
been able to prove that the halteridium is the sexual 



Proteosome. 



Halteridium. 



t>70 INFECTION AND IMMUNITY. 

stage of a trj-panosome which multiplies in the common 
mosquito — Culex pipiens — and after a complicated mi- 
gration through the body of the mosquito is again in- 
troduced by its bite into the blood of the owl, where, 
after a period of sexual multiplication, it is transformed 
into the well-known male and female halteridium." 

IF. TRYPANOSOMIASIS. 

Genns Grubv created the genus Trypanosoma in 1843, 
soma, when lie gave the name 01 1 rypanosoma sanguinis 
to a flagellate protozoon which he found in the 
blood of frogs. Since that time similar organisms 
have been found in the bloods of many animals and 
the genus Trypanosoma has grown to considerable 
dimensions. It is not improbable, however, that 
a number which now bear independent names will 
be shown to be identical. This suggests itself par- 
ticularly in relation to trypanosomiasis in horses, 
in which the infections are known under four sep- 
arate names in different countries, and the para- 
sites are given separate specific names. The study 
of these infections is so } T oung and has been prose- 
cuted in such widely separated countries that the 
existing chaos is quite natural and can be adjusted 
only as time and circumstances permit of close 
comparative study. Until such a time the prevail- 
ing views as to independence of species and of in- 
fections must be recognized. 

Trypanosomas vary a great deal in size and mor- 
phology. Roughly, they are from one to five mi- 
crons thick and from fifteen to forty-five microns 
long, including the flagellum. All species possess 
active eel-like movements, some traveling rapidly, 
others slowly. A long, actively-motile flagellum 
projects from the anterior end, and where it joins 






TRYPANOSOMIASIS. 671 

the cell body is continuous with an "undulating 
membrane/' which extends along a border of the 
organism to a point near the centrosome or mi- 
cronucleus in the posterior portion of the cell. 
The centrosome is sometimes spoken of as anala- 
gous to the "eye spot" of some other protozoa. The 
undulating membrane is more or less wavy or 
folded and its breadth varies. The centrosome pre- 
sumably has a close relationship to the undulating 
membrane, and, through the latter, with the flagel- 
lum. The nucleus is in the anterior portion of 
the parasite. In relation to some species a con- 
tractile vacuole is spoken of. An endoplasm and 
an ectoplasm may be differentiated. 

Division of trypanosomes is nearly always longi- 
tudinal, rarely transverse. In the process of longi- 
tudinal fission the order of division of the differ- 
ent parts of the cell is as follows : 1, Centrosome ; 
2, flagellum; 3, nucleus and protoplasm (Laveran 
and Mesnil) . After division has occurred the two 
cells may remain attached at their posterior ends 
for some time. By a repeated division of young 
cells, the posterior ends remaining attached, ros- 
ettes are said to be formed. Others consider ros- 
ette formation as a phenomenon of agglutination. . 
Possibly both phenomena occur. 

Koch and others have described sexual repro- 
duction in the tsetse-fly. 

Koch divides the trypanosomes into two classes classification. 
as to constancy in respect to: (1) morphology; 
(2) virulence; (3) host. This classification is 
best represented by the accompanying table from 
Nocht and Mayer. 



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TR YPA XOSO MIASIS. 



673 



TRYPANOSOMIASIS IN MAN. 

Nepveu in 1898 first found trypanosonies in Tj-ypanoso- 
the blood of man in Algiers in eight cases. His ob- Fever. 
servations were passed over temporarily. The para- 
site bears his name (T. nepveui). Again in 1901 
Forde discovered similar parasites in Western 
Africa (Gambia), and since that time a number 
of cases of "Gambian fever" or trypanosomatic 
fever in man have been imported. In this in- 
stance the parasite was called T. gambiense by Dut- 
ton and T. hominis by Manson. The disease is 
said to follow the bite of a tsetse-fly (Glossina 
palpalis), at least in some instances. The tissues 
around the bite become inflamed and in from a 
few days to two weeks recurring attacks of fever 
set in, and a patchy and ringed erythematous erup- 
tion appears on the skin. Forcle gives as the 
chief clinical findings in his case: (1) the irregular 
intermittent temperature; (2) the edematous con- 
dition of the face and lower extremities; (3) the 
rapid and variable pulse and respiration, unac- 
companied by any evident cause; (4) loss of 
weight, with marked debility, wasting and lassi- 
tude; (5) the persistence of these symptoms and 
their resistance to treatment. The parasites are 
most numerous in the blood at the time of the 
febrile attacks. Eecovery has not been reported. 

Sleeping sickness has been endemic in certain sleeping 
districts of Africa for a long time, and, although 1C ness * 
confined to a very limited district at one time, it ap- 
pears now to have extended to distant parts. Speak- 
ing of trypanosomatic fever and sleeping sickness 
collectively, Ruata says that while originally con- 
fined to a small district in Western Africa between 



674 



INFECTION AND IMMUNITY. 



the latitudes 15' North and 15' South, it is now 
found one thousand miles up the Congo (Bangola, 
Stanley Falls) and in East-central Africa on the 
shores of the Victoria Nyanza Lake. "Now it ex- 
tends from the mouth of the Katonga River 
through Uganda (1901, Cook), Kome Island, 
Busaga, Buvuma, Kavirondo, Kisumu, Lumbwa, 
Homa, Kasagunga, Lusinga Island, the eastern 
shores of the lake, joining the south of the bound- 
ary river Gori in the Udemi district of the Sultina 
of'Obo" (Ruata). 
occurrence. Its extension supposedly has been facilitated by 
rapid transit. "The disease is most prevalent 
amongst the inhabitants of low-lying shambas (ba- 
nana and potato plantations) in places along the 
shores of the Victoria Nyanza, or in wooded dis- 
tricts not far from the water" (Christy). Those 
living on high ground are much less infected than 
those living in the low moist places near water. A 
great deal of stress is laid on its close association 
with inland bodies of water. 

It apparently has no relation to sex, age, sea- 
sons, food or drinking water, and is related to oc- 
cupation only in so far as the occupation carries 
one into the low places mentioned. 

At one time (1891) Manson advanced the idea 
that sleeping sickness is caused by the minute 
Filaria perstans. It has since developed that this 
parasite occurs in 70 per cent, of the natives in 
certain districts, and that sleeping sickness may 
occur in areas in which Filaria perstans does not 
exist; Manson has abandoned this view. A num- 
ber of investigators also found cocci in the cerebro- 
spinal fluid, but this occurred very rarely during 
life and at a late stage of the disease ; such organ- 



Trypano- 
sonies in 
Sleeping 
Sickness. 



TRANSMISSION. 



075 



Tsetse 
Ply. 



isms are probably secondary or agonal invasions 
in spite of their rather frequent occurrence. Fur- 
ther investigations by Castellani disclosed the pres- 
ence of a trypanosome (T. castellani) in the cere- 
brospinal fluid of a large percentage of the cases, 
and a little later Bruce found this organism in all 
the cases he had examined. This observation has 
been confirmed so many times that the trypan- 
osome is now generally considered as the cause of 
the disease. 

Sleeping sickness is not contagious in the or- 
dinary sense, and Bruce furnishes very strong 
evidence that it is transmitted by the bite of 
a tsetse-fly (Glossina palpalis). The distribu- 
tion of the disease corresponds to the habitat of 
this fly, and Bruce transferred the infection to 
monkeys by means of flies which had bitten those 
suffering from sleeping sickness. Gray and Tul- 
lach have demonstrated the presence of trypano- 
somes in the alimentary canal of tsetse flies which 
were allowed to feed on the blood of patients with 
sleeping sickness. 

A pronounced lethargy or somnolence is the symptoms 
most striking clinical feature of the disease. "The 
appearance of the somnolent condition is preceded, 
often for a long time, by prodromal signs, which 
are so characteristic that the patient's neighbors 
cannot possibly be deceived as to the fate that 
awaits him. The victim complains of weakness, 
langour, dejection, disinclination for work, head- 
aches, particularly localized over the occiput, a: 
sensation of weight in the head and giddiness*. 
His eyelids tend continually to close and he has a f 
tendency to go to rest at unusual hours of the day ;. 
for this purpose he seeks out lonely quiet spots> 



676 



/ \ FECI !<>.\ AND JMML Ml ) . 



where he spends a long time in dozing'' (Scheube). 
For some time he is able to resist the somnolence, 
and when aroused gives intelligent answers. He 
eventually acquires an unsteady gait and walks 
about like a drunken man. The temperature of 
the body appears to be lowered, although irregular 
attacks of fever occur. The somnolence gradually 
becomes more intense, the patient grows very weak, 
the pulse small and thready, respiration difficult, 
the edema seen in trypanosomatic fever is rather 
constant, incontinence of the urine and feces may 
develop; the patient commonly dies after passing 
into a stale of deep stupor. Convulsions and pa- 
ralyses are noted; the mind usually is clear when 
the patient is conscious, although maniacal at- 
tacks and delusions are occasionally noted. The 
cervical and superficial lymphatics are frequently 
but not constantly enlarged. A papulo-vesicular 
eruption is quite characteristic and persistent and 
the skin becomes very dry. The incubation period 
varies from six to eighteen months, and the som- 
nolent state from three to twelve months. Recov- 
ery rarely occurs. 

The essential anatomic change is meningo-en- 
cephalitis, the soft membranes being thickened, 
containing a milky fluid and the vessels of the pia 
and brain being surrounded by an extensive infil- 
tration of mononuclear leucocytes. 

The discovery of trypanosomes in sleeping sick- 
ness suggested that trypanosomatic fever may 
really represent the long prodromal stage of sleep- 
sickness. [ n g sickness. This view has been greatly strength- 
ened by a case reported by Manson in which a 
typical case of trypanosomatic fever was seen to 
pass into t}'pical and fatal sleeping sickness. The 



3Iening;o- 
Encephaliti.s. 



Identity of 

Trypano- 
somatic 
Fever and 
Sleeping 



SLEEPING SICKNESS. 677 

wife of a missionary in upper Congo was bitten 
by a tsetse-fly, and following an inflammatory re- 
action at the seat of the bite, she developed and ran 
a long course of trypanosomatic fever. After from a 
year and a half to two years of remittent attacks 
of fever, the organisms being found in the blood 
repeatedly, she grew weaker, became somnolent 
and died in a comatose condition. The anatomic 
changes at autopsy were typical of sleeping sick- 
ness. Some who are not quite willing to accept the 
unity of the two diseases suggest that the sleeping 
sickness may have been superimposed on trypano- 
somatic fever. 

Assuming that the two conditions represent dif- 
ferent stages of the same disease, we would have 
to recognize trypanosomatic fever as the first stage 
and the lethargy of sleeping sickness as the second. 
If this proves to be correct the name of T. nepveui 
should be retained for the organism and the other 
names dropped (T. ganibiensc, T. liominis, T. 
castellani) . 

It is believed that T. castellani is a distinct The 
species of trypanosome. It is hardly possible to as- 
sociate it with nagana, since sleeping sickness and 
nagana do not coincide in their distribution, and, 
moreover, the morphology and pathogenicity of 
T. castellani differ from that of T. hrucei. The 
former is not infectious for the "donkey, ox, 
guinea-pig, dog, pup, goat and sheep" (Ruata). 
T. castellani is from 18 to 25 microns long and 
from 2 to 2.5 broad. Its morphology in general 
is like that of other trypanosomes, although there 
are sufficient differences to establish its independ- 
ence. Its motility is rather slow, and in contrast 
to other trypanosomes it moves in the direction of 



678 INFECTION AND IMMUNITY. 

its non-flagellated end. The failure to find any 

distinctive difference between this organism and 
T. neprevi (T. gambiense) is an additional point 
in favor of the unity of trypanosomatic fever and 
sleeping sickness. 

TRYPANOSOMIASIS IN ANIMALS. 
On account of the prevailing general interest in the 
subject, the more important trypanosomatic infections 
in animals and the corresponding parasites will be 
sketched briefly. 
Geueral Musgrave and Clegg speak of certain general symp- 
Symptomut- toms which are common to surra, nagana, mal de caderas 
o oft>. an( j j our j nej as follows: "After an incubation period, 
which varies in the same class of animals and in those of 
different species as well as with the conditions of infec- 
tion, and during which the animal remains perfectly 
well, the first symptom to be noticed is a rise of tem- 
perature, and for some days a remittent or intermittent 
fever may be the only evidence of illness. Later, the 
animal becomes somewhat stupid; watery catarrhal dis- 
charges from the nose and eyes appear; the hair becomes 
somewhat roughened and falls out in places. Finally, 
the catarrhal discharges become more profuse and the 
secretion more tenacious and even purulent; edema of 
the 'genitals and dependant parts appears; a staggering 
gait, particularly of the hind parts, comes on and is fol- 
lowed by death." 
Infectious- The incubation period varies from a few to several 
"ltioo?/ days. Pronounced anemia develops, the method of de- 
struction of the erythrocytes being unknown. Lymphatic 
enlargement is the rule, and during the incubation period 
the parasites probably undergo great proliferation in the 
lymph glands. It is somewhat characteristic that mas- 
sive invasion of the blood streams occurs periodically. 
With a paroxysm of fever their numbers increase in the 
blood, and during the intermission they decrease and 
may be so few as not to be found microscopically. Even 
when few or no parasites are found in the circulation, 
however, the blood usually is infectious for other ani- 
mals. During the intermissions it is possible that they 



CULTIVATION OF TRYPANOSOMAS. 



679 



are largely within the lymph glands or other internal 
organs. The cause of these variations is not known, and 
it can not be said now that they are related to cycles of 
development like those of the malarial parasites. Voges 
suggests that they may represent the establishment of 
successive periods of temporary immunity (mal de 
cameras). These are only general features, and varia- 
tions occur in infections in different animals and by dif- 
ferent parasites. 

Trypanosoma lewisi, recognized in the blood of the rat 
by Lewis in 1879, and given its present name by Kent 
in 1882, infects wild rats throughout the world, and in 
some localities a very high percentage of the animals are 
infected. The parasite is readily found in the peripheral 
blood (as from the tail), where a large number may be 
present in a single field of the microscope; sometimes, 
however, prolonged search is necessary for their discov- 
ery. Its dimensions vary: from 1.4 to 3 microns in diam- 
eter, and from 10 to 25 microns in length, according 
to different observers. It is of lancet-form, pos- 
sesses a finely granular endoplasm and a clear 
ectoplasm, and from the latter spring the flagel- 
lum and the undulating membrane. "The for- 
mer (flagellum) is about as long as the body itself; 
it originates at the posterior end of the animal in a 
granule-like structure, called the flagellar root, extends 
forward as a marginal thickening of the undulating 
membrane and becomes free only at the anterior end of 
the animal from which it extends into the surrounding 
endomedium as a flagellum" (Dofleiri). At its posterior 
extremity the parasite ends in a sharp point. In its an- 
terior portion it contains a strongly staining nucleus; a 
contractile vacuole is not described. Its motility is, per- 
haps, more active than that of any other trypanosome, 
and in a fresh mount of rat's blood it may move across 
the field so rapidly as to be followed with difficulty. 

Division takes place by longitudinal fission (rarely 
transverse), and by repeated division rosettes are 
formed. 

Novy and McNeal succeeded in cultivating this organ- 
ism artificially on a medium consisting of rabbit's blood, 
2 parts, agar, 1 part. The growth occurs in the con- 



Trypanoso- 
miasis of 
Rats. 



Cultivation. 



080 INFECTION AND IMMUNITY. 

densation lluid, and the organisms were carried through 
many generations. In cultures they vary greatly in size 
(from 1 to 00 microns in length). "The existence of the 
small forms accounts for the fact that we have repeat- 
edly been able to infect rats with Berkefeld filtrates of 
such cultures." It is remarkable that so many of the 
rats which harbor the parasites appear to be perfectly 
healthy. However, the animals not infrequently die 
from the infection, and in some instances fairly severe 
epidemics have been noted. The infection is found also 
in the hamster, a European rodent, and in white rats. 
White mice arc Busceptible to inoculation (Dollein). 
lagana. Trypanosoma Irucci, found by Bruce in 1894 in the 
blood of animals suffering from nagana or the tsetse-fly 
disease in Zululand is somewhat different morphologi- 
cally from T. leivisi, being more worm-like in form, hav- 
ing a blunt posterior extremity, less motility and greater 
pathogenicity. "The undulating membrane is broader 
and more plicate, the protoplasm colors more easily and 
more deeply'* than in T. Icu-isi. Its length is said to 
vary, depending on the animal which harbors it, being 
largest in the rat and shorter and thicker in the dog. 
Its dimensions as given by Laveran and Mesnil are 1 to 
1.5 by 26 to 27 microns. Its structure is similar to that 
of T. leicisi, containing a nucleus near the middle of the 
body and a deeply staining centrosome in the posterior 
portion in or near which the flagellum has its origin. 
A contractile vacuole lies anterior to the centrosome. 

Natural infection (nagana) with this organism occurs 
in horses, cattle, mules, and also in some wild animals, 
as camels, buffaloes and hyenas. It is, however, a tropi- 
cal disease, occurring chiefly in various parts of South 
Africa. Nearly all animals are susceptible to artifi- 
cial infection by the injection of diseased blood. 
Tsetse ^he distribution of nagana corresponds with the dis- 
F1 >*« tribution of the tsetse-fly, and Bruce discovered that this 
fly, after feeding on the blood of an infected animal, 
transfers the disease to others by biting. Horses, asses, 
cattle and hogs were infected artificially in this way, but 
man appears not to be susceptible. It is assumed, but 
perhaps not definitely proved, that no other fly or insect 
transmits the disease. Immediately after it has fed on 



CULTIVATION OF TRYPANOXOMES. 681 

infected blood it is capable of transferring the disease; 
hence, further development of the parasite in the tsetse- 
fly is not essential for its continued infectiousness, and, 
indeed, it is not certain that any further development 
occurs. 

Nagana presents a remittent or intermittent type of 
fever, catarrhal secretion from the nose and eyes, sub- 
cutaneous edema, particularly of the abdominal region, 
prepuce and posterior extremities, roughening and shed- 
ding of the hair, marked emaciation, weakness and ane- 
mia develop, and the animal dies in a state of exhaus- 
tion. The spleen is greatly swollen, the red corpuscles 
are diminished in number, and the urine may be blood 
stained. The parasites are found in enormous numbers 
in the blood. 

The disease is almost invariably fatal. It may last 
for weeks or months in horses, and even much longer in 
cattle. It occurs not infrequently in epidemic form, 
wiping out the horses and cattle of infected regions. In 
wild animals it is suggested that the disease may be 
more chronic, and the shifting of such animals may 
serve to introduce the infection to new regions, but only 
to such regions as harbor the tsetse-fly. 

Novy and McNeal cultivate T. orucei on a medium Cultivation. 
similar to that used for T. lewisi. The former is more 
exacting in its conditions for growth, preferring a me- 
dium containing blood and agar in a ratio of two to one 
or three to one. Cultures were kept alive for at least 
one hundred days through eight generations, although 
virulence was soon lost. 

Trypanosoma evansi is the name given by Steele to a Surra 
parasite discovered by Evans (1880), in India, in the 
blood of horses suffering from surra. It has the same 
general morphologic features as T. orucei, with dimen- 
sions from 1 to 3.5 or 4 microns by 20 to 35 microns, in- 
cluding the flagellum (Musgrave and Clegg). It eon- 
tains a nucleus and possibly a contractile vacuole. The 
whole posterior extremity is contractile, according to 
Musgrave and Clegg, and this may also be true of other 
trypanosomes. Its motility is moderate and eel-like. It 
differs from the trypanosome of rats (T. lewisi) in its 
larger diameter and in its greater pathogenicity; T. 



682 INFECTION AND IMMUNITY. 

evansi is pathogenic for "nearly all animals." It is 
longer than T. brucei. 

Surra a fleets horses chiefly, and has caused immense 
losses in India and in the Philippine Islands. In India 
it is certainly transmitted by certain flies, and the same 
probably is true in the Philippines. Musgrave and Clegg 
demonstrated also that lleas may be of great importance 
as carriers. By this means they were able to transfer 
the disease from dog to dog, rat to rat, and rat to dog. 
They frequently found the parasites in native rats and 
believe that this animal may serve as a host in which the 
disease is maintained. Cattle are susceptible to infec- 
tion, but the disease is less malignant in them and runs 
a long course; hence, they may be an important factor 
in maintaining an epidemic. The disease is also trans- 
mitted from horse to horse. In India, camels, elephants 
and buffaloes also suffer from the disease. Surra resem- 
bles nagana in its clinical and anatomic aspects. 

Donrino. Doflein gave the name of Trypanosoma equiperdum to 
an organism described by Rouget in horses and asses 
suffering from dourine. Laveran and Mesnil call it T. 
rougetii. According to Rouget, the parasite resembles 
T. brucei closely. Doflein (1901) states that a nucleus 
and vacuole have not been seen. Dourine occurs in 
Algiers, southern France, Navarre and in the Pyrenees 
districts of France and Spain. The infection is trans- 
mitted by coitus and is limited largely to animals which 
are used for breeding. Ulcerations, particularly of the 
genitals, are characteristic. That it is not transmitted 
by insects may be due to the absence of suitable insects 
from these localities. The identity of dourine with 
surra or nagana is not yet determined. It is said to be 
more chronic than surra. Doflein recognizes the organ- 
ism as an independent parasite. Infection may be trans- 
ferred to dogs, white mice and other animals. 
Mai ue Trypanosoma equinum (Voges) or T. elmassianii is 

Caderas. the parasite found in mal de caderas, a disease of horses 

in South America, resembling surra, nagana and dourine. 

T ~ .. Two different species have been found in the blood of 

Infections r 

of otiier South African cattle: T. theileri (Bruce, 1902) and T. 

Animals, transvaaliense (Laveran and Mesnil, 1902). The char- 
acteristic feature of the latter is the location of the 



G I L TI 1 A TWN OF TR YPA N080ME8. 



683 



centrosome near the nucleus near the center of the para- 
site. The following trypanosomes are found in fish: 
T. cobitis, T. carassii, T. remakii, T. solece, T. borrellii; 
the following in birds: T. avium, T. eberthii. T. balbianii 
occurs in oysters, T. rotatorium in frogs. 

Between various animals and the different try- 
panosomes a number of examples of natural im- 
munity are known. The extent to which man is 
susceptible to sleeping sickness is not known, but 
since the disease may occur in Europeans as well 
as in native Africans, it is probable that suscepti- 
bility is general. Laveran and Mesnil state that 
sheep, deer and cattle which have recovered from 
nagana have an active immunity to the disease, 
and it is thought that the immunity of some ani- 
mals (e. g., cow) may be increased by injecting 
infected blood. Koch, and also Schilling, have at- 
tempted to render trypanosomas suitable for vacci- 
nation by passing them through asses, and a cer- 
tain degree of success was reported. The serums 
of actively immunized animals do not exert a pro- 
nounced protective or curative action, although 
they may in some instances prolong the incubation 
period. Human serum has a certain protective 
and curative power for rats and mice which have 
been inoculated with the parasite of nagana. In 
some instances immune and normal serums kill 
trypanosomes, as shown by rapid loss of mobility. 

A most interesting bit of experimental therapy 
is that of Ehrlich and Sachs in curing and pro- 
tecting mice against mal de caderas by injecting 
and feeding "trypanroth," a synthetic dye. The 
dye was less efficient in experimental nagana and 
in trypanosomatic infections of rats, guinea-pigs 
and dogs. The immunity and cure established in 



Imimimty. 



"Ti-ypini- 
rotli." 



684 IXFECTIO* AND IMMUNITY. 

this way is very temporary and is to be referred 
to a reaction caused in the body rather than to a 
direct effect on the parasites. The latter are not 
killed by the dye in test-tube experiments. "One 
may conceive of the action of a trypanroth in this 
way, that as a result of a fresh injection of the 
dye a reaction takes place in the animal's body, 
which leads to the death of the trypanosomes; the 
reaction products possess only a temporary char- 
acter and cease to he formed as soon as the dye 
is disposed of.* 

Laveran reports a favorable influence on try- 
panosomiasis in mice and rats by a combined treat- 
ment with sodium arsenite and "trypanroth." 

When a dose of trypanroth which is insufficient 
to cause complete disappearance of trypanosomes 
is given, the remaining organisms become immune 
to the further action of the drug. It is of impor- 
tance, therefore, to give the largest dose which is 
non-toxic for the patient. At present, two new 
preparations of Ehrlich, trypanosan and agridi- 
num, which are highly trypanocidal, are being 
tried in combination with arsenophenylglycin. 

III. TEXAS FEVER. 

Texas fever of cattle may be considered briefly as a 
well-established example of piroplasmosis. 
The Th * Smith and Kilbourne (1893) discovered a pear- 
Parasite, shaped protozoon {Pyroplasma bovis) , which occurs in 
pairs in the erythrocytes of infected cattle. The para- 
site measures from 2 to 4 microns long by 1.5 to 2 
microns broad, the smaller ends of the pairs lying in 
apposition. The organisms have a rapid but rather coarse 
ameboid movement. About 1 per cent of the corpuscles 
are invaded ordinarily, but in fatal cases the proportion 
may rise from 5 to 10 per cent. The method of prolifera- 
tion of the parasite has not been followed out definitely. 



TEXAS FEVER. 685 

According to Smith and Kilbourne, numerous minute 
motile forms (coccus-like bodies) penetrate the corpus- 
cles and eventually reach the pear-shaped form. The 
breaking up of the adult pear-shaped parasites into such 
small forms has not been observed. 

A characteristic symptom of Texas fever is the pro- 
nounced hemoglobinuria which has given to the disease 
the additional name of hemoglobinuric fever. 

The disease is transmitted by means of a tick {Boophi- 
lus bovis). The six-legged larvae fill themselves with 
blood, and in about eight days have been changed into 
eight-legged nymphae. In eight days more they have 
changed into fully-formed sexual animals, and, after 
filling themselves with blood and after having been im- 
pregnated, they drop off the cattle and lay their eggs. 
Larvae hatch from the eggs in from 3 to 4 weeks, and 
the former are again ready to attach themselves to 
cattle ( cited from Kossel ) . Inasmuch as infected ticks 
transmit the parasites to their offspring, the bites of the 
larvae are able to give rise to the disease in cattle. A 
mature tick may deposit from 2,000 to 4,000 eggs. It 
has not been possible to transmit the disease to other 
species. 

The disease is endemic in the southwestern states, Transmission, 
and the cattle in that region are supposed to acquire an 
immunity similar to that described by Koch in relation 
to malaria. Presumably the cattle first acquire the dis- 
ease when they are young, and those which withstand it 
show resistance to the infection in later life. Cattle 
from uninfected districts are more susceptible than these 
coming from localities in which the disease is endemic, 
and the latter even when apparently healthy may intro- 
duce the disease into new herds. This is done through 
transportation of the ticks. 

Partially successful attempts at active immunization 
have been made, and in Australia this is practiced on 
a fairly extensive scale. Five to ten' cubic centimerp of 
blood, taken from an infected animal, during the course 
of the disease or after recovery has been established, are 
injected into non-immune cattle. The disease is thereby 
reproduced in the latter with typical parasites in the 
blood. If the blood is taken from animals which have 



68G INFECTION AND IMMl MTV. 

recovered, a milder infection results than when the blood 
of an actively infected animal is used (Pound, cited by 
Kossel). The resulting immunity is not an absolute one, 
however, and the percentage of mortality is fairly high. 
According to Dodson, the serum of animals which have 
completely recovered has no protective power for other 
animals. 

For prophylaxis it is important to free the cattle 
from ticks (as by an oil bath) and to avoid infected 
fields. If cattle are kept from an infected pasture for 
two years, the ticks die out very largely (Morgan). 

IV. AMEBIC DYSENTERY. 

Ameba. Amebae are unicellular animal organisms which 
contain one or more nuclei, a "contractile" vacuole, 
a granular endoplasm and a tougher more hyaline 
ectoplasm, having the power of locomotion by 
means of pseudopodia or by a gradual flowing for- 
ward of the cytoplasm. They nourish themselves 
by digesting bacteria and other lower organisms or 
solid particles of decaying matter, which they in- 
gest after the manner of phagocytes. They pro- 
liferate by division of an adult cell into two daugh- 
ter cells, and certain of them reach a cystic stage 
in which hundreds of endospores are formed 
(Amcvba proteus). Some of them utilize higher 
animals as hosts only occasionally, while others 
are known only as parasites. They frequently are 
encountered in the intestines of mice, frogs and 
other animals. 
Distribution. Amebse are widely distributed in nature, exist- 
ing to the depth of 2 meters in tropical soils, in 
the water of springs and wells and practically all 
surface waters (hot countries), and in stagnant or 
sluggish waters in higher altitudes. They exist on 
hay, fruits and vegetables of all kinds, especially 



AMEBIC DYSENTERY. 687 

those grown on or near the earth; e. g., beets and 
lettuce. 

Encystation takes place under certain unfavor- Resistance. 
able conditions, and in this condition the parasites 
withstand a temperature of — 15° C. for twenty- 
five days (Musgrave and Clegg), and desiccation 
for from ten to fifteen months. A temperature of 
50° C. kills the vegetable and encysted forms. 
Sunlight for three hours and the £-ray kill them 
readily in the vegetable form, but not so readily 
when they are encysted. Most chemical bacteri- 
cides destroy them, although they show a particu- 
lar resistance to alkalies, even 20 per cent, sodium 
hydrate (Frosch), and strong acids. They resist 
the action of 0.2 per cent, hydrochloric acid, i. e., 
the acidity of the stomach contents. Quinin 
(1/2500 of the hydrochlorate) is strongly germi- 
cidal for Amoeba coli. 

Under artificial conditions amebse proliferate cultivation. 
in the presence of other micro-organisms, and 
suitable mixtures they may be kept alive in- 
definitely on slightly alkaline bouillon agar. 
The only condition in which amebse are found 
unassociated with bacteria is in the liver ab- 
scesses which occur as a complication of amebic 
dysentery. It is true that the bacteria may have 
been present originally, but in their absence it is 
supposed that enzymes normally present in the 
liver stimulate the growth and proliferation of the 
parasites. Amebse show a peculiar selective property 
for certain bacteria, although their affinities may 
be gradually modified. Amoeba coli apparently pre- 
fers those organisms which flourish in the human 
intestines (B. coli, B. typhosus, Sp. choleras, Staph, 
pyog. aureus). Almost any strain will, however, 



688 INFECTION AND IMMUNITY. 

grow with a variety of bacteria. Growth occurs 
only on the surface of the agar plates. When a 
pure strain of ameba is grown with a single species 
of bacterium the culture is spoken of as a "pure 
mixed culture." 

Amebic dysentery is primarily a disease of the 
tropics, where the natural conditions are favorable 
for the growth of the amebae and their conveyance 
to man. 
Ameba First found by Lambl (18G0), then by Cunning- 
ham and Lewis (1870), the organisms were de- 
scribed more accurately and given the name of 
Amoeba coli by Loach (1875). Losch recognized 
them as the cause of a chronic form of dysentery, 
but it was Kartulis, in particular, who found the 
amebae constantly in the discharges and ulcers of 
the disease, and also in the liver abscesses which 
accompany the infection. Since amebae demand 
the presence of living bacteria for their growth, 
their independent pathogenic nature has been ques- 
athog-e- tioned by many who assume that the bacteria are 
the primary agents in causing the intestinal lesions 
and that the amebae are only incidental or second- 
ary factors. Many others, and particularly Mus- 
grave and Clegg, consider that amebae have essen- 
tial pathogenic properties and are the primary 
agents in producing amebic d} r sentery. By the 
feeding of encysted cultures grown with other or- 
ganisms, Musgrave and Clegg reproduced the dis- 
ease typically in many monkeyj. In one instance 
the amebae were fed in conjunction with cholera 
vibrios; typical dysentery developed and during 
the course of the disease the vibrios disappeared 
from the stools. The vibrio alone proved to be 
non-pathogenic when fed to monkeys, and on this 






AMEBIC DYSENTERY. G89 

account they held the amebae to be the sole cause 
of the dysentery. 

According to Schaudinn and Craig, amebce are 
of two types. One of non-pathogenic character 
(Entamoeba coli) found by Craig in 50 per cent, 
of normal stools ; the other pathogenic (Entamoeba 
histolytica) . 

According to Schaudinn, the two organisms dif- Lesions. 
fer in morphology and method of reproduction. 
Walker fails to confirm these observations. 

The principal lesions occur in the large intes- 
tine, in which are found round or oval ulcers with 
infiltrated or undermined edges. The ulcers may 
increase in size, or coalesce with others, and cause 
the sloughing of large areas of the mucosa or even 
of the muscular coats. The organisms are found 
in the intestinal contents, on the surface of the 
ulcers, in the infiltrated base and edges, and in the 
underlying tissues. They have been found as- 
sociated with both chronic and acute appendi- 
citis. Amebic liver abscesses are not infrequent 
in those regions in which the disease is endemic. 
The organisms probably extend to the liver from 
the intestines through the lymphatic or portal 
vessels. Not infrequently the association of the 
amebse with bacteria is missed in the abscesses, 
and in these instances a "cold" abscess containing 
much necrotic material and detritus is produced. 
If contaminated with bacteria the abscesses have 
a more purulent character. 

Suitable prophylaxis against amebic infection is Prophylaxis. 
suggested by the known distribution of these or- 
ganisms. Of principal importance is the use of fil- 
tered or boiled waters and the avoidance of un- 



GOO INFECTION IND IMMUNITY. 

cooked vegetables in regions in which the disease 
is endemic, as in the Philippine Islands. 
Immunity. From the fact that foreigners going into tropical 
countries are more susceptible to infection than the 
natives, it is concluded that the latter have some 
natural (or acquired) immunity to the disease. 
Children are said to be less susceptible than adults 
and in them the disease yields to treatment more 
easily. There is no serum therapy for the infec- 
tions. The salts of quinin in strengths of from 
1-1500 to 1-750 are amebicidal when injected into 
colon. 

V. SARCOSPORIDIA. 

Morphology. Sarcosporidia are unicellular parasites which are 
found within the muscle cells of some animals, but 
very rarely in man. They are more or less tubular 
or oval in shape and are frequently referred to as 
Miescher's tubules. Their size varies greatly and 
certain species may reach a length of two centi- 
meters. When well developed they possess two 
capsules — a dense outer capsule, which is perfor- 
ated with minute canals (?) directed toward the 
center of the parasite, and an inner thin hyalin 
membrane. Both represent differentiated ecto- 
plasm (Doflein). The endoplasm, even in young 
cells, gives rise to numerous small nucleated 
spheres (pansporoblasts), which increase in size 
and each of which eventually becomes multinu- 
cleated and forms numerous kidney or sickle- 
shaped, nucleated sporoblasts. Each sporoblast 
finally gives rise or is changed into a well-charac- 
terized spore with a membrane and a nucleus. 
This process takes place first in the central part 
of the parasite, but eventually extends to the ends 



BALANTIDIUM COLI. 691 

as well. The central part of the old parasites con 
tains only the empty network of endoplasm, the 
spores having disappeared, and a section at this 
point strongly resembles that of a tubule. 

The parasites are nourished through osmosis. 
None of the forms have definite motility. When 
the parasite outgrows the muscle cell which con- 
tains it, it is freed and becomes an intercellular 
parasite. Eather vague references are made to 
tumor-like formation as a consequence. 

Sarcosporidia have been found only in verte- occurrence. 
brates, particularly in mammals; most often in 
sheep and hogs, but also in the horse, ox, mouse, 
rat. The muscles adjacent to the alimentary tract 
are involved principally (esophagus, intestines, 
diaphragm and abdominal muscles) and on this 
account it is supposed that infection takes place 
through the intestines. The exact method of in- 
oculation is not known. 

Sarcocystis lindemanni {Sarcocystis hominis or 
Gregarina lindemanni) is the only sarcosporidium 
definitely identified in man. The parasites were 
as large as 1.6 millimeters long and 170 microns 
broad. They possessed a thin capsule, thickened 
at the ends. The spores were banana-shaped and 
from 8 to 9 microns long. The organisms were 
found in the muscles of the larynx. 

VI. BALANTIDIUM COLI. 

B. Goli is an infusorian (ciliate), with a more 
or less oval body, mouth opening and a short 
pharynx, is covered rather uniformly with short 
cilia, and presents longitudinal striations. It con- 
tains a bean-shaped chief nucleus and a secondary 
nucleus and two vacuoles on the right side. It meas- 



692 INFECTION AND IMMUNITY. 

ures from 70 to 100 microns in lengths and from 
50 to 70 in breadth. Proliferation is through sim- 
ple division. Conjugation lias Leon noted. Invo- 
lution cysts are Bypherical and surrounded by a 
druse membrane. 
Pathosenir The parasite is found in the intestines of the hoc; 
as well as in man, and the iormer may be its nor- 
mal host. It occurs also in sewage waters and has 
been found in drinking water. Infections have 
been noted in those having nothing to do with hogs. 
The organism- may reach the intestines of man in 
an encapsulated state (?). It is found in diar- 
rheal conditions in man rarely, and the question 
is still open as to whether the parasite is able to 
cause enteritis independently or whether it merely 
aggravates and prolongs an enteritis due to other 
causes. 

The cecum and colon show the principal changes 
at autopsy, and are of an inflammatory and ulcera- 
tive nature. 

A smaller species, B. minutum, has also been 
observed in the intestines of man. 

VII. CERCOMONAS INTESTINALIS. 

Morphology. This organism is small and colorless, the form 
spherical or oval. The single flagellum is for the 
most part very large and is situated at the anterior 
end (in the direction in which the parasite 
moves) ; the posterior end is long drawn out and 
is subject to changes in form. Sharp pseudopodia 
are sometimes formed. The nucleus lies in the 
anterior half of the body, and either here or on the 
sides are one or more vacuoles. A mouth opening 
is not differentiated, but at the base of the flagel- 
lum food is taken in at a particular point through 



TRICHOMONAS. G93 

a vacuole. Proliferation takes place through con- 
jugation, binary division and the formation of 
swarm spores ( ?) within encysted forms. They 
abound in fresh water and in infusions of grasses. 

They are not of great parasitic importance, al- significance. 
though cercomonas has been found in the intes- 
tines, especially in inflammatory conditions (chol- 
era, typhoid), in pulmonary gangrene, putrid plu- 
ritis, and several forms have been observed in other 
animals. 

It is not yet certain that cercomonas may be an 
independent cause of enteritis. 

VIII. TRICHOMONAS. 

Rather small, of a general pear-shape, rounded Morphology. 
or pointed anterior end, and possessing three or 
four long flagella. When only three flagella are 
present an undulating membrane surrounds the 
body like a spiral beginning at the base of the 
flagella and may prolong itself into a flagellum. 
The posterior extremity is moderately pointed, a 
nucleus lies in the anterior end, and toward the 
posterior are several non-contractile vacuoles. 
Methods of proliferation unknown (Doflein). 

Two species are found in man. Trichomonas 
vaginalis: possesses three flagella and an undu- 
lating membrane, and is of large size (from 15 to 
25 microns in length). It is found in the vaginal 
mucus, when of acid reaction, in a large percent- 
age of women (Dolflein), particularly in vaginal 
catarrhs. It disappears in an alkaline reaction. 

Trichomonas hominis s. intestinalis: also pos- 
sesses three flagella and an undulating membrane, 
but is smaller than T. vaginalis. It is found as a 
parasite in the human intestines, particularly in 



094 INFECTION AND IMMUNITY. 

diarrheas (typhoid, cholera, mucous colitis, etc.,) 
and inhahits especially the upper and middle por- 
tions of the intestines. It is evacuated in consid- 
eral numbers following administration of cathar- 
tics. It appears not to be of much pathogenic sig- 
nificance, but finds in the liquid stools and in an 
alkaline reaction conditions which favor its prolif- 
eration. It may be transmitted as a contagion 
(Epstein). 

Other species of trichomonas occur in the intes- 
tines of different animals. 
other Other less important flagellates are: Lamblia 
intestinaliSj found in the intestines of many ani- 
mals and in man in Germany, Italy, Russia and 
Sweden; Bodo urinarius (Cystomonas urinarius, 
Plagiomonas urinaria), found in the urine in cys- 
titis (Kiinstler). 

IX. COCCIDIOSIS. 

Coccidia are essentially cell parasites, preferring 
the epithelial cells of the intestines and liver, al- 
though they may be carried to other organs. They 
have an alternating asexual and sexual cycle of 
development. The young sickle-shaped and nu- 
Life cycles, cleatod sporozoite penetrates an epithelial cell, 
grows in size, and the nucleus subdivides many 
times to form new young cells, which eventually 
escape again as sickle-shaped sporozoites. This 
asexual process is called schizogony. Several stages 
of schizogony may follow successively, but event- 
ually the organisms lose their proliferative power 
unless they are fortified by a sexual cycle. In the 
sexual cycle (sporogony) some of the sporozoites 
become differentiated into larger granular cells 
(female) and others into smaller cells (male). 



COCCIDIOSIS. 695 

Of these two cells the male eventually divides into 
many flagellated microgametes, each of which is 
able to penetrate and fertilize a female cell (macro- 
gamete). The female cell then forms a capsule, 
becomes an oocyst, divides into sporoblasts, each 
of which eventually forms sickle-shaped spores, species. 
which when liberated are again called sporozoites. 
Several species are recognized, depending on the 
number of spores formed by the oocyst. In some 
instances the spore formation takes place in the 
outer world, and when the oocysts are ingested the 
sporozoites are liberated. 

Coccidium cuniculi s. oviforme is a frequent 
parasite in the intestines and liver of the rabbit, 
occurs occasionally in the same organs in man from 
association with rabbits (?), and causes a hemor- 
rhagic dysentery in the cattle of some countries 
(Switzerland). Horses, goats and swine may also 
be infected. 

Spore formation takes place outside the host. 
The oocyst is discharged in the feces and produces 
four spores, each of which forms two sporozoites. 
A new host is infected by the ingestion of spores. 

Diarrhea and emaciation result from infection Results of 
of the intestines, and in the liver cheesy nodules 
(coccidia nodules) are formed, containing para- 
sites, degenerated cells and proliferated epithe- 
lium. A papillomatous proliferation of the epi- 
thelium of the bile passages and intestines may be 
produced. 

Coccidium bigeminum, a coccidium in which 
the oocyst divides into two spore-containing cysts, 
has been found in man several times. 



696 l\ri:cil<>\ \\I> IMMUNITY. 

X. KALA-AZAR. 

Kala-azar, or febrile splenomegaly, is a tropical 
disease, especially of India and China, associated 
with great enlargement of the Bpleen, often of the 
liver, extreme cachexia and anemia. The disease 
was formerly looked on as a malarial cachexia. 

Both Leischman and Donovan described bodies 
in stained preparations of splenic pulp and 
ascribed to them an etiological significance. These 
observations have been confirmed repeatedly. The 
bodies are small round mass of cytoplasm, which 
with the Romanowski stain is colorless. Two 
masses of chromatin, one much smaller than the 
other, take a purplish Btain. The whole body is 
from 2 to 3 microns in diameter. Eogers suc- 
ceeded in cultivating the organisms in blood 
Blightly acidified with citric acid and incubated at 
C. In this way a flagellated form was ob- 
tained which is similar to trypanosomes in mor- 
phology. The classification, however, is not yet 
certain. The organism is distributed throughout 
the body, but is most numerous in the spleen, bone 
marrow, and liver. 

Tatton succeeded in obtaining growth of the 
parasite in the stomach of the bed bug, and it 
seems probable that transmission occurs in this 
way. Eogers, acting on this supposition, was able 
to reduce the number of cases by ridding the 
houses of bed bugs. 



CHAPTER XXX 
GROUP VII 

DISEASES OF DOUBTFUL OK UNKNOWN ETIOLOGY. 



Negri. 



I. HYDROPHOBIA. 

Following the investigations of Pasteur, in 
which it was found that the virus of hydrophobia 
exists in the central nervous system in pure cul- 
ture, the conditions seemed favorable for the dis- 
covery of the specific agent. As in the case of 
many other diseases, various bacilli, cocci, yeasts 
and so-called protozoa have been described as the 
cause, but satisfactory proof of their etiologic role 
has not been provided. 

Certain protozoon-like bodies (Negri bodies) Bodies of 
found by Negri in the ganglionic cells, are of a 
suggestive nature. Their average diameter is 
about five microns, but it varies between one and 
twenty-seven microns. They possess a "round, 
oval, elliptical, or coarse triangular form" (Marx), 
are differentiated into a central granular and a 
peripheral structure and may be surrounded by a 
doubly-contoured membrane. Negri considers these 
bodies specific for hydrophobia and reliable as a 
basis for anatomic diagnosis. -They are found par- 
ticularly in the pyramidal cells in the cornu Am- 
monia, the cells of Purkinje in the cerebellum, 
and the large cells of the cerebral convolutions. 
Many others have confirmed the findings of Negri, 
and it is now generally conceded that the bodies 



698 INFECTION AND IMMUNITY. 

are specific for rabies, and of great diagnostic 
value. Against the hypothesis that these bodies 
are the cause of hydrophobia, the following points 
are cited : The distribution of the Negri bodies 
does not correspond with the greatest concentra- 
tion of the virus in the nervous tissue, the latter 
being most abundant in the medulla and pons 
where the Negri bodies are encountered rarely. They 
present certain analogies with "protoplasmic in- 
clusions" seen in other conditions, as in carcinoma, 
variola, etc. Remlinger found that the virus 
passes through appropriate Berkefeld filters, and 
for this reason Schiider holds that the bodies of 
Negri, being too large for filtration, can not be 
considered as the specific organism. The view of 
Schiider may be criticized, since the smallest 
Negri bodies are so minute that their filtration 
would seem to be possible. Nevertheless, it must 
remain doubtful whether bodies one micron in di- 
ameter, the proliferation of which has not been 
proved, may be considered as parasites. The hy- 
pothesis of Negri is hardly on a satisfactory basis 
at present. Remlinger considers the bodies as 
"involution forms" of the tissue cells which have 
been invaded by the true parasite. 
Fiitembiiity The filterability of the virus argues for its ultra- 

of Virus. . J ? 

microscopic size. By means 01 nitration one may 
isolate it even from brains which are badly decom- 
posed, and the method renders it possible to ob- 
tain pure cultures for purposes of immunization. 
Inoculation with filtered virus is sometimes fol- 
lowed by a prolonged incubation period which may 
depend on the retention of many of the organisms 
by the filter. A similar effect was produced by 
Hogyes by inoculating with diluted virus. 



HYDROPHOBIA. 699 

By prolonged centrifugation of an emulsion of 
infected nervous tissue the overlying fluid loses its 
infectiousness. 

The possibility that the organism secretes a sol- Toxin. 
uble toxin is important from the standpoint of im- 
munization. A number of observers, particularly 
Babes, and Heller and Bertarelli, noted that fil- 
trates of infected nervous tissue sometimes cause 
emaciation, paralyses and eventual death without 
producing a disease which is transmissible to other 
animals. The organism is without doubt toxic, 
but these results give us no idea of the nature of 
the toxin. 

The virus of hydrophobia as contained in the Resistance 
central nervous system of infected animals exhib- 
its strong resistance to chemical germicides. Five 
per cent, carbolic acid destroys it in fifty minutes, 
1 per cent, in three hours, and 1-1000 corrosive 
sublimate in three hours (Marx). It resists the 
action of putrefactive bacteria, and has been found 
virulent in animals which had been buried for two 
to four weeks, even when the brain was putrid. Di- 
rect sunlight destroys it, however, in a very short 
time. According to Tizzoni and Bongiovanni, the 
rays of radium have a destructive action on the 
virus. It is less resistant to heat, being destroyed in 
one-half hour at a temperature of 52-58° G. 
(Hogyes), hut is not affected by the temperature 
of liquid air for three months. Chlorin destroys 
it very rapidly. It is gradually weakened by 
desiccation, as first shown by Pasteur, the virus 
probably undergoing gradual death rather than 
mere attenuation. It is said to be attenuated by 
the action of the gastric juice and by the bile. 
When the nervous tissue is emulsified in glycerin, 



700 INFECTION AND IMMUNITY. 

virulence is retained for months (Roux). On the 
other hand, glycerin appears to destroy the viru- 
lence of filtrates (Di Vesica). 

street \iru* Pasteur gave the name of street v^rus (virus 
a ims. de rue) to that obtained from the nervous tissue of 
dogs in which the disease develops spontaneously. 
When the street virus is injected subdurally into 
the rabbit the latter develops hydrophobia only 
after an incubation period of from two to three 
weeks, Ef, however, this vims is passed from one 
rabbit to another, its virulence gradually increases 
until the incubation period decreases to six days. 
Ai this poinf it is called fixed virus (virus fixe), 
and its virulence can not be further increased. 
Passage through the cat, fox and wolf also in- 
creases virulence. On the other hand, by passing 
it repeatedly through the monkey (Pasteur), the 
chicken (Kraus) or the dog it becomes attenuated 
for the rabbit and virulence may be lost entirely. 
i. ..xv vim- Although virus fixe represents its highest degree 

Fixed virus, of virulence for rabbits, there is good reason for 
believing that repeated passage through the rab- 
bit decreases the virulence of the virus for man. 
In other words, street virus is more infectious for 
man than fixed virus. This may to some extent ac- 
count for the success of the Pasteur treatment. 
Ferran, indeed, uses unaltered virus fixe for the 
protective inoculation of man. 

Distribution By means of inoculation experiments the virus 
the Hody. may be demonstrated invariably in the brain, 
spinal cord, and usually in the salivary glands and 
saliva of animals wdiich have died of the disease. 
These tissues are specifically affected, and the virus 
probably proliferates in them. By one or another 
observer its presence in the following organs and 



Infection. 



TRANSMISSION. 701 

excretions has been demonstrated : Suprarenal 
gland, lachrymal gland, vitreous humor, urine, tes- 
ticular secretion, lymph, milk, in the peripheral 
nerves and cerbrospinal fluid. Marx states that 
it has not been found in the liver, spleen, blood and 
aqueous humor. Courmont and Nicolas found it, 
however, in the aqueous humor of rabbits after 
death. The possibility of postmortem invasion of 
this fluid has been suggested. It has been found 
occasionally in human saliva during life, and at 
the site of the wound following death (Pace). 

Hydrophobia is transmitted almost exclusively Means of 

/> Tnfontim. 

by the bites of infected animals, the virus being 
conveyed in "the saliva. Accidental inoculation may 
occur in handling infected tissues. The virus does 
not penetrate the intact skin, and it is customary to 
consider a bite as harmless unless the continuity 
of the skin is broken. Experimentally, infection 
has- been caused by placing the virus on the mu- 
cous membranes of the conjunctiva, nose and 
mouth, in the absence of discernible lesions. Pace 
mentions a man who contracted the disease after 
his rabid dog had inserted the tip of its tongue in 
his (the patient's) nose. But one authentic ex- 
ample of transmission from man to man is found 
in medical literature. This occurred through kiss- 
ing or biting, during coitus. In rare instances it 
seems to have been transmitted from the mother 
to the fetus in rabbits. 

The dog is the most common carrier of hydro- 
phobia. In some countries (Eussia, Hungary) rabid 
wolves cause many infections. The disease has been 
conveyed by the bite of the cat, mouse and horse, 
and possibly by the skunk in some of our western 
states. The dog is, however, the natural host of 



702 INFECTION LAD IMMUNITY. 

the parasite, and either by his bite or by experi- 
mental inoculation practically all animals, at least 
mammalians, may be infected. 
incubation The incubation period in animals varies from 
two weeks to several months. In man it varies 
between twenty and sixty days usually, but may be 
as 6hort as seven or ten days, or as long as twenty 
months (rare). In children it is shorter than in 
adults. The location of the bite is also of impor- 
tance in determining the length of incubation. It 
is shortest following wounds of the head and neck, 
somewhat longer when the injury is in the hand or 
arm, and still longer when in other parts of the 
body. The degree of laceration is also a factor, de- 
pending possibly on the introduction of larger 
quantities of virus, and on larger surfaces for its 
absorption. The bite of the wolf is said to be most 
virulent, and next in virulence is the bite of the 
cat and dog. 

Not all who are bitten by rabid animals develop 
hydrophobia. Correct figures on this point are dif- 
ficult to obtain, since in many instances the ani- 
mals are only suspected of being rabid. According 
to Hogyes, from 15 to 16 per cent, of those who 
are bitten contract hydrophobia. The percentage 
is much higher following bites by the wolf. The 
disease is invariably fatal to man. 

The symptoms of hydrophobia in man differ in 
no essential respects from those seen in animals. 
Diagnosis The immediate determination of hydrophobia 
in dogs which have bitten man is of the greatest 
importance. In many instances the behavior of the 
animal is sufficiently characteristic to justify clin- 
ical diagnosis of the disease. The disposition of 
the animal changes suddenly, it ceases to play, eats 



in Dogs. 



.PATHOLOGY. 703 

various indigestible substances, as glass, iron and 
wood, utters pathognomonic (?) long-drawn-oat 
howls, may become ferocious, or, on the other 
hand, quiet and sullen. At autopsy the meninges 
and nervous tissue are congested if the disease is 
advanced, and the indigestible substances men- 
tioned may be found in the stomach, although the 
latter finding has little or no diagnostic importance. 

A number of histologic changes have been de- so-caiied 
scribed as characteristic. Among these are the i^sfonS. 
bodies of Negri, described above. Eemlinger at- 
taches a great deal of importance to them as a 
means of diagnosis. Babes describes perivascular 
nodules of lymphoid cells (Wutknotchen) in the 
medulla and cord. The lesion of Van Gehuchten 
consists of a proliferation of the endothelial cells 
(neuronophages) surrounding the ganglionic cells, 
the latter at the same time undergoing atrophic 
and degenerative changes. This change is most 
marked in the cervical ganglia. One group of ob- 
servers finds these lesions constant in animals 
which have died of hydrophobia, but they may be 
absent if the animal is killed during the course of 
the disease; hence their absence does not exclude 
the diagnosis of hydrophobia. Others have found 
similar changes in other diseases. Metchnikotf, 
it will be remembered, observed the destruction of 
ganglionic cells, by neuronophages in aged dogs 
(page 309). 

We are hardly able at present to consider these 
changes as pathognomonic. Particularly in early 
stages of the disease they may be absent. The bite 
of a rabid dog is infectious in from two to four 
days in advance of the development of symptoms, 
and autopsy performed at this time may show 



704 l\ I '!■:< ■/ /"\ AND IMMl Mi) . 

neither gross nor microscopic changes which arc 
characteristic. 
Extension A great deal of experimental work which can not 

Nerves, be given in detail shows conclusively that the virus 
is conveyed to the central nervous system by means 
of the peripheral nerves. The conditions then are 
similar to those in tetanus with this exception: In 
hydrophobia the Jiving virus reaches the central 
nervous system, whereas in tetanus the bacilli re- 
main at the site of the wound. This condition ex- 
plains the shorter incubation period in hydropho- 
bia, as in tetanus, when the infection atrium is 
near the central nervous system (e. g., face). When 
the infection is introduced into any particular 
part of the body surface, the virus is first demon- 
strable in the corresponding segment of the cen- 
tral nervous s; - Although transmission by 
the nerves is the rule, infection may be accom- 
plished in rabbits by intravascular injection. On 
the whole, however, infection is closely associated 
with the wounding of nerves. It has indeed 
been shown that if wounding of nerves is entirely 
avoided, as in intraperitoneal injections into rab- 
bits (Marx) the full virulent nervous tissue may 
be used for immunization. A single injection of a 
large quantity brought about immunity in twelve 
days. 

The muzzling of dogs is a general prophylactic 
measure, which should be enforced in communities 
in which hydrophobia is known to occur. No mat- 
ter how thoroughly the cauterization and antisep- 
tic treatment of wounds is carried out it can in no 
case be depended on to destroy the virus. Even 
within five minutes the virus may be carried to a 
point which is beyond the reach of the cautery. In 



PASTEUR TREATMENT. 705 

spite of this fact, however, cauterization should 
not be neglected, even when the Pasteur treatment 
can be instituted at once. The greater the quantity 
of virus introduced by the bite the shorter will be 
the incubation period, and there is good reason to 
believe that cauterization (actual cautery) prop- 
erly carried out destroys a sufficient amount of 
virus to prolong the incubation period. A long 
incubation period is greatly in favor of the success 
of the Pasteur treatment. 

In communities in which hydrophobia is known 
to be endemic, in all cases of dog bite accompanied 
by penetration of the skin, the patient should re- 
ceive the Pasteur treatment. 

Pasteur's first protective inoculations were car- Preparation 
riecl out with virus which had been attenuated by Pasteur 8 f 
passage through the monkey. The virus fixe ob- 
tained from the rabbit, as described above, was 
soon substituted for that of the monkey. In order 
that an antirabic institute may continuously have 
on hand a sufficient amount of vaccine, it is neces- 
sary to inoculate two or three rabbits daily. For 
this purpose an emulsion of the medulla of a rab- 
bit which has died of hydrophobia is inoculated be- 
neath the dura mater. A short time before the 
animals would die of the disease, they are killed 
by bleeding, and the spinal cords removed with all 
possible precautions for asepsis. Each cord is cut 
into two parts and each part suspended in a prop- 
erly constructed jar which contains solid potas- 
sium hydrate. After the jar is sealed desiccation 
is allowed to proceed for fourteen days, at the end 
of which time the infectiousness of the tissue has 
so decreased that it is suitable for the first injec- 
tion. The vaccine should be free from bacteria. 



Treatment. 



Treatment. 



TOG 1XFECTION AND IMMUNITY. 

\ ording to Harvey and McKendrick, the degree 
of infectivity of dried rabic virus is a "function 
of the loss of weight in water mused by the dry- 
ing." 
Technie of As is well known, the Pasteur prophylactic 

I ...ii I ....... I * m 

treatment consists of the subcutaneous injection 
on successive days, of suitable quantities of virus 
/i.rr. prepared as described above, beginning with 
the cord which has been desiccated for fourteen 
days and gradually using fresher cords until viru- 
lent virus has been inoculated. The vaccine is pre- 
pared for use by emulsifying one centimeter of a 
cord in 5 C.C. of salt solution or some "artificial 
serum. n and in a single treatment from 1 to 3 c.c. 
of this emulsion is injected, usually into the sub- 
cutaneous tissue of the anterior abdominal wall. 
In this region there is less likelihood of injuring 
large nerves, and local complications, which, how- 
ever, occur rarely, are of less consequence. 

The rapidity with which one should pass from 
the fourteen-day cord to fresh virus depends on the 
urgency of the case. When there is good reason to 
suspect a short incubation period, or when some 
days have followed the bite an "intensive" treat- 
ment should be used ; in other cases the progression 
may be slower. The following conditions augur 
a short incubation period : Bites of children, who 
are more susceptible than adults, and in whom 
the injuries usually are on the face; bites on the 
face and neck in all cases; lacerated wounds in 
which there is a larger surface for absorption of 
the virus. The influence w r hich proper cauteriza- 
tion exerts on the incubation period was mentioned 
above. 



PASTEUR TREATMENT. 707 

The table on page 708, taken from Marx, illus- 
trates a "light" and an "intensive" treatment. 

This scheme is variously modified in different 
institutes, especially in the direction of a more 
rapid progression to virulent material. 

Other methods of attenuation are also used, as other 
the following: Heating emulsions of fresh virus Attenuation. 
at 58° C. for different lengths of time, or at dif- 
ferent temperatures (80° to 30° C.) for ten min- 
utes (Babes-Puscari) ; digestion of virus with nat- 
ural or artificial gastric juice (Tizzoni and Cen- 
tanni) ; the use of fresh but very dilute virus 
(Hogyes). Ferran, in Barcelona, inoculates man 
with the fresh unaltered virus fixe, and in nearly 
2,000 cases but two cases of hydrophobia devel- 
oped. This indicates clearly the low infectious- 
ness of virus fixe for man. 

The tendency at present is toward the use of 
fresh rabic virus for the prophylactic treatment of 
hydrophobia. This is the method of Hogyes, and 
also of Ferran. Hogyes* first injection consists of 
3 c.c. of a 1 to 10,000 or 1 to 8,000 dilution of 
the fresh rabic cord, and gradually within the next 
fourteen days the concentration is increased until 
1 c.c. of a dilution of 1 to 100 is given. 

In order to obtain a basis of comparison for 
the different methods of treatment Harvey and 
McKendrick have proposed an arbitrary unit of 
standardization for rabic virus. For this purpose 
they agreed to consider that 0.2 c.c. of a 1 per 
cent, emulsion of the fresh virus fixe contains 
1,000 units. From this it follows that 0.2 c.c. 
of a 1 to 1,000 emulsion would contain 100 units, 
and 0.2 c.c. of a 1 to 1,000 dilution, 10 units. 



708 



INFECTION AND I \I.\U Ml ) . 



The first dose in the Bogyea method according to 
this scale represents L50 units. Naturally those 
methods in which dried virus is used for at Least 
pari of the treatment can no< be expressed in units 
until tlif infective value of the cords dried for dif- 
ferent periods is determined. This was investi- 



Light. 


Intensive. 


I>HV Of 


Age of 


Amount of 


Day of 


Age of 


Amount of 


Treat- 




Emulsion 


Treat- 


l>ri.'<l (\>r-l 


Emulsion 


ment. 




Injected. 


ment. 


in Days. 


Injected. 




- u 


S 






fit 


3 


1 


3 






18 


3 


_ 


12 


3 


1 




12 


3 


- 


11 


3 






11 


8 


8 


* 10 


8 






10 


3 




8 







( .i 


8 


4 




:; 






! 


3 
3 






2 

• 


3 




6 

6 


2 


8 




2 


4 


R 


2 


7 




2 


5 


5 


2 


8 


4 


g 


6 


1 


2 







1 


7 


8 


1 


10 


5 


•j 


- 


4 


2 


11 


5 


•> 


9 




1 


12 


4 


8 


10 


B 


2 


13 


4 


2 


11 


5 


2 


14 


3 


•» 


12 


4 


o 


16 


8 


2 


13 


4 


2 


16 


5 


2 


14 


3 


9 


IT 


4 


2 


15 


2 


2 


18 


3 


2 


16 


5 


2 








17 


4 


2 








18 


3 


g 








19 


5 


2 








20 


4 


2 








21 




3 


2 



gated by Harvey and McKendrick and their con- 
clusions were as follows: "(1) Emulsion of the 
nine-day cord is little if at all infective in a dose 
of 0.2 c.c. of a 1 in 5 emulsion. (2) Emulsion 
of five-day cord is infective in minimal time in a 
dose of 0.2 c.c. of a 1 in 100 emulsion, but be- 
come less so or not at all in a dose of 0.2 c.c. of 



PASTEUR TREATMENT. 709 

a 1 in 200 emulsion. (3) In the same way the 
M. I. D. (minimum infective dose) for an emul- 
sion of three-day cord is 0.2 c.c. of a 1 in 200 
emulsion. (4) The M. I. D. of two-day cord is 
not greater than 0.2 c.c. of a 1 in 1,000 emulsion 
and probably not less than 0.2 c.c. of a 1 in 2,000 
emulsion. (5) The M. I. D. of one-day cord is 
not greater than 0.2 c.c. of a 1 in 4,000 emulsion 
and almost certainly not less than 0.2 c.c of a 
1 in 8,000 emulsion (the lower accepted limit of 
fresh material). (6) Fresh material is infective 
(M. I. D.) in a dose of 0.2 c. c. of a 1 in 8,000 
dilution and may be so in considerably higher 
dilutions even up to 1 in 40,000, but with such 
high dilutions the experimental errors become so 
great as to preclude any more exact fixation of 
the M. I. D." 

Although these results are not mathematically 
exact, it is probable that they may be used as a 
working basis, and from them it is possible to 
calculate the number of units in a given amount 
of rabic cord dried for different periods. Harvey 
and McKendrick estimate that in both the Pas- 
teurian method and that of Hogyes little more 
than 25,000 units are administered during the 
course of treatment. 

It seems unnecessary at this date to quote sta- 
tistics to show the value of the Pasteur treatment. 
Observations indicate that immunity is not fully 
established until about fourteen days after the 
completion of the treatment, and in a certain num- 
ber of cases the disease develops before this time 
has passed. The number of deaths after this pe- 
riod is exceedingly small and has grown less with 



710 IXFECTIOy AXD IMMUNITY. 

improved teclmic. In 1886 the number of deaths 
which occurred after fifteen days had passed 
amounted to 0.94 per cent.; in 1902 to 0.18 per 
cent. 
immunity The immunity established by the Pasteur treat- 
propertieM. ment is, in all probability, antimicrobic in nature. 
The serum of both man and animals, after immun- 
ization, is able to destroy the infectiousness of rabic 
nervous tissue, i. e., the serum is rabicidal (Babes 
and Lepp, 18S9). The technic of Kraus and 
his co-laborers is well adapted to show the rabi- 
cidal properties of the immune serum. Rabid ner- 
vous tissue is made into an emulsion with salt 
solution in a dilution of 1 to 100, and then filtered 
through paper to remove coarse particles of tissue. 
To quantities of 0.5 to 1.0 c.c. of this emulsion 
varying amounts of fresh immune serum are added, 
and after eighteen hours' contact the mixtures are 
injected into rabbits to determine the degree of 
infectiousness. Small quantities of rabicidal sub- 
stance may be detected in this way. 

Natural resistance to hydrophobia does not go 
hand in hand with the antirabic power of an ani- 
mal's serum. Old pigeons, for example, develop the 
disease following intracerebral injection of the 
virus, although their serum is not rabicidal. 

Babes and Lepp also showed that the immune 
serum has protective powers which are analogous 
in their efficiency with those of bactericidal serums. 
Babes advocates and practices the mixed method 
of immunization in severe cases, immune serum be- 
ing injected in addition to the virus. The serum 
has little or no curative value. 



YELLOW FEVER. 711 



II. YELLOW FEVER. 



Yellow fever is peculiarly an American disease, 
and it has reached other continents (e. g., Spain) 
only in accidental ways and for brief periods. It 
is possibly endemic in certain portions of West 
Africa (Sierra Leone), to which it was probably 
carried from the Antilles (Schenbe). Scheube 
regards the Antilles as the birthplace of yellow 
fever. Knowledge of it extends only to the middle 
of the seventeenth century, at which time it 
surely existed in the West Indies. The dis- 
ease has on several occasions been carried to 
Spain by vessels returning from Cuban ports. 
Until very recent times it was endemic in 
Cuba, especially Havana, and in Vera Cruz 
and other Spanish- American ports it has prevailed 
extensively. From such points extension frequent- 
ly takes place into adjacent tropical or subtropical 
regions, or even into temperate localities during 
the summer months. In the latter part of the 
eighteenth century Philadelphia suffered very se- 
verely. Baltimore was attacked similarly and Bos- 
ton to a less degree. Other northern ports, e. g., 
New York, have experienced attacks of limited 
duration, the disease, presumably, being intro- 
duced by means of infected ships. 

In addition to our southern coasts and that of 
Mexico, the Atlantic coast of South America has 
been infected as far south as Buenos Ayres, and 
likewise the western coast of Mexico and Peru. In 
the eighteenth century the coast of Spain and 
Portugal suffered severely, but since that time 
only minor epidemics have occurred in these coun- 
tries. Epidemics frequently have appeared on 
ships after they had left infected ports. 



INFECTION AND IMMUNITY. 



Bncilliin 
Irtcroides. 



The Mosquito 
Theory. 



The Southern States were invaded repeatedly in 

the last decade of the eighteenth century, in 1803, 
1S05, 1853, 1SG7, 1873, L878, 1905, and in lesser 
s at other times, in all ninety-six times. The 
si epidemics were those of 1853 and 187S. 

The many microbes which have heen cited as the 
cause of yellow fever need not be described. The 
\us vcteroides of Sanarelli, which had at- 
tains! more prominence than any other. was shown 
by Sternberg, by Reed and Carroll and by the more 
recent work on the mosquito theory, to hear no 
causal relationship to the disease. According to 
and Carroll it is identical with the hog-chol- 
era bacillus. 

The monumental work of Reed, Carroll, Agra- 
monte and Lazear (1900), the last of whom lost 
his life from yellow fever, has made it possible 
to replace accurate knowledge of the epidemiology 
and prophylaxis of yellow fever and, to a certain 
extent, of its etiology, for many incorrect ideas 
which hail prevailed up to that time. 

The conception that yellow fever is transferred 
from one person to another by mosquitoes was 
first advanced positively by Carlos Finlay. a 
Cuban physician, in 1881, although several Ameri- 
can physicians had long before noted the preva- 
lence of mosquitoes during yellow fever outbreaks 
(Rush, 1793; Weightman/ 1839 ; Wood, 1853; 
Barton. 1853). Finlay reported the transmission 
of the disease, experimentally, by the bites of mos- 
quitoes which had fed on yellow-fever patients, 
and stated that light attacks which followed the 
bites resulted in the establishment of immunity. 
The subsequent observations of Reed and his co- 
workers indicate, however, that Finlay's technic 



ST EGO MY I A FAS CI AT A. 



713 



was such that he could not possibly have produced 
experimental fever, and that the development of 
the disease in his subjects was purely a coincidence. 
The reason for this will appear below. 

Having satisfied themselves that Bacillus icte- 
roides is but an accidental organism in yellow 
fever, and that it is found under normal condi- 
tions as well, Eeed and his associates began work 
on the mosquito hypothesis of Finlay. The first 
positive result was obtained in the case of Dr. Car- 
roll. Carroll "was bitten at 2 p. m., Aug. 27, 1900, 
by Stegomyia fasciata. This particular mosquito 
had bitten a severe case of yellow fever on the 
second day of the disease, twelve days before; a 
mild case of yellow fever on the first day of the 
attack, six days preceding; a severe case of yellow 
fever on the second day of the attack, four days 
before; a mild case of yellow fever on the second 
day of attack, two days before inoculation." After 
an incubation period of three days, Carroll devel- 
oped typical and severe yellow fever, from which 
he recovered. A similar result in one other case 
was reported at this time, and later Camp Lazear, 
with mosquito-proof houses, was established for the 
continuation of the study. The experiments of 
Reed and his co-workers, and confirmatory work by 
Guiteras and the French commission, can not be 
described in this place. We may feel sure, how- 
ever, that with all the conditions of experimenta- 
tion under absolute control the following points 
have been determined with scientific certainty: 1. 
Yellow fever may be transferred from a* patient to 
a non-immune by the bite of a mosquito — Stego- 
myia fasciata — which has previously fed on a 
yellow-fever patient. 2. In order that the mos- 



The "Work of 
Reed, Carroll, 
Etc., With 
Stegromyia 
Fasciata. 



Important 
Facts Which. 
Have Been 

Learned. 



714 INFECTION AND IMMUNITY. 

quito become infected it is necessary for him to 
feed on yellow-fever blood within the first few 
days (three days) of the fever. 3. The mosquito 
can not transfer yellow fever directly and imme- 
diately from the patient to a non-immune, but it 
is necessary for a period of not less than twelve 
days to elapse before he becomes infectious. When 
this time has been reached the insect continues in- 
fectious for at least fifty-seven days and probably 
throughout his life. 4. Yellow fever can not be 
transferred by "fomites." 5. The subcutaneous in- 
jection of yellow fever blood into a non-immune 
produces yellow fever, hence the infecting agent 
a in the circulation. G. The serum of a yel- 
low fever patient, after being diluted and filtered 
through a Berkefeld filter (Reed and Carroll) or 
Chamberland B porcelain filter (Rosenau, Parker, 
Francis and Beyer) is infectious, hence the in- 
fecting agent at some stage of its development is 
very minute, possibly ultramicroscopic. 7. "An 
attack of yellow fever produced by the bite of a 
mosquito confers immunity against the subsequent 
injection of the blood of an individual suffering 
from the non-experimental form of this disease" 
(Reed, Carroll and Agramonte). 8. The period of 
incubation usually is three days, but may vary 
within the limits of from two to six days. 9. "A 
house may be said to be infected with yellow fever 
only when there are present within its walls con- 
taminated mosquitoes capable of conveying the 
parasite of the disease." 10. "The spread of yel- 
low fever can be most effectually controlled by 
measures directed to the destruction of mosquitoes 
and the protection of the sick against the bites of 
these insects." 11. Xo mosquito other than Stego- 



and Stego- 

myia. 



STEGOMYIA F ASCI AT A. 715 

tnyia fasciata has been found capable of transmit- 
ting the disease, and analogies suggest the proba- 
bility that no other insect is concerned. 

These discoveries explain many facts in rela- Epidemiology 
tion to yellow fever which had been obscure hither- 
to. For example, yellow fever is a tropical and 
subtropical disease only because Stegomyia fas- 
ciata breeds in tropical and subtropical climates. 
The disease is found in low, moist localities rather 
than in the high and dry, because the mosquito in- 
habits the former and not the latter. Yellow 
fever dies out with the first severe frost or on the 
advent of cool weather because these conditions 
either kill the mosquito or cause him to hibernate. 
The advent of an initial case of yellow fever in a 
suitable region is followed by the appearance of the 
disease in epidemic form only after a period of two 
or three weeks, because the mosquito first becomes 
infectious in about two weeks after it has fed on 
yellow fever blood; this may correspond with a 
certain stage of development of the as yet unrecog- 
nized parasite. The observation often made that 
yellow fever, like malaria, is not contagious in the 
ordinary sense, in spite of its rapid extension, is 
readily understood, as is the irregular method in 
which the disease spreads. It is now clear why the 
disinfection of fomites has never been able to 
check the advance of an epidemic, and why the 
ordinary quarantine measures which did not take 
the mosquito into consideration were not effective 
in keeping the disease out of a favorable port ; and 
by a favorable port is meant one which can harbor 
Stegomyia fasciata. These discoveries also ex- 
plain how yellow fever could be stamped out of 
Havana, Texas and New Orleans by prophylactic, 



716 INFECTION AND IMMUNITY. 

hygienic and quarantine measures, which had aa 

their objects the destruction of the mosquito and 
its breeding places and prevention of the infection 
of the mosquitoes by suitably screening the pa- 
tients. 
Distribution j^ [g {] llls SGen [\ ia ^ th e epidemic occurrence of 

at m <-u«mii ▼ in . l 

yellow fever is strictly associated with the distribu- 
tion of Stegomyia fasciata. Howard, in Bulletin 
No. 4U of the Public Health Reports, gives this 
distribution as known on Sept. 10, 1905, and pub- 
lishes a map showing the region which the insect 
may be expected to inhabit. 

st. oiata has been found in the following 

localities in the United States (Howard): 

Virginia: Virginia Beach, Norfolk, Lynchburg, Dan- 
ville, Richmond. Kentucky: Lexington, Middlesboro, 
Louisville, Richmond. Illinois: Cairo. Tennessee: 
Nashville, Knoxville, Clarksville, Chattanooga, Memphis, 
Columbia, Decherd, Athens, Bristol. Arkansas: Hot 
Springs, Helena. Louisiana: Ruddock, New Orleans. 
Baton Rouge, Napoleonville, Covington, Hammond, 
Shreveport, Franklin, Morgan City, New Iberia, Patter- 
son. Mississippi: Pass Christian, Summit, Quarantine 
Station, Vieksburg, Clarksdale, Tutwiler, Bekoni, Holly 
Springs, Jaekson, Wonona, West Point, Tupelo, Corinth, 
Agricultural College, Biloxi. Alabama: Mobile, Decatur, 
Auburn, Tuscumbia, Huntsville, Yazoo City. Georgia 
Atlanta, Pelham, Augusta, Savannah, Brunswick. 
Florida: Bnrrancas, Key West. Texas: Galveston, 
Houston, Victoria, San Diego, Tyler, Laredo, Austin 
San Antonio, Corsicana, Brownsville, Alice, Colorado, 
Dallas, Paris, Edna, Fort Bliss (El Paso), Fort Ring- 
gold (Rio Grande-Ludlow). South Carolina: Charles- 
ton, Columbia, Fort Fremont, Sullivan's Island. Ari- 
zona: Nogales. Maryland: Baltimore (Carter) — breed- 
ing in fresh water on fruit wharf. North Carolina: Beau 
fort, Winston, Raleigh, Greensboro, Charlotte, Salisbury, 
Indiana: Jeffersonville. Missouri: St. Louis. 



STEGOMYIA F ASCI AT A. 



717 



Reed and Carroll found the larvae of stegornyia Breeding 
"(1)' in rain-water barrels; (2) in tin cans that Li?e e cy?ie. 
had been used for removing excreta and which 
still contained a small amount of fecal matter; 

(3) in sagging gutters containing rain water; 

(4) in cesspools; (5) in tin cans placed about 
table legs to prevent the inroads of red ants; (6) 
in the collection of water at the base of the leaves 
of the agave americana; (7) in one end of a 
horse trough that was in daily use." These in- 
stances are cited to show the general character of 
the places in which the eggs and larvae of stegornyia 
may be found. The eggs are deposited during the 
night, in about seven days after the ingestion of 
blood, and "in pairs, in groups of three or more 
or singly/' to the number ol forty-seven on the 
average (Eeed and Carroll). The eggs are very 
resistant to drying and extreme cold ( — 17° C). 
With a favorable temperature they hatch in from 
three to seven days ; the larval stage lasts for seven 
days, the pupal two days, the total cycle being 
completed in about twelve days. As in the case of 
anopheles, only the female stegornyia sucks blood. 
The insect prefers the hours from 3 p. m. to 9 a. 
m. for feeding, but is most active from 4 p. m. 
to midnight. "In captivity the hungry impreg- 
nated female will bite at any hour of the day or 
night." In a state of freedom it will not bite a Biting 
second time for from five to seven days. It ap- 
pears not to bite when the temperature is lower 

than 62° F., another factor in the subsidence 
of yellow fever with the advent of cool weather. 
For further details concerning the morphology, 
biology and habits of stegornyia consult Howard 
on "The Mosquito"; Reed and Carroll, "The Pre- 



71- INFECTION AND IMMUNITY. 

vention of Yellow Fever," Medical Record. Oct. 
86, 1901; Parker, Beyer and Pothier, "Report 
of Working Party No. I" Yellow Fever Institute 
Bulletin No. 13, 1903, Washington. 
importation Yellow fever eases and stegomyia work together 

i»v Snips. . o 

in the extension of the disease just as malarial 

cases and anopheles do in the extension of ma- 
laria; for the principles involved the chapter on 
malaria may be consulted. Of particular interest 
is the importation of the disease by means of ships, 
since the invasion of the United States usually 
comes about in this way. It is frequently stated 
that ships lying one-half mile from shore are safe 
from yellow fever; Grubbs, however, believes that 
imyia may reach vessels lying within fifteen 
miles of the shore if the wind is favorable. The 
based readily hoards a vessel lying in an infected 
port and may remain there at least during a sev- 
enteen da; It may also breed in suitable 
barrels or tanks of water on the ship. Under these 
conditions it is readily understood how a ship, 
leaving a harbor with a healthy crew, may be at- 
tacked by yellow fever a few days after leaving 
port; and how any quarantine measure at a new 
port which does not involve the destruction of the 
mosquitoes on the boat and the protection of the 
patients from the bites of mosquitoes is inadequate. 
Resistance As stated, the nature of the virus is unknown. 
Its nlterability was mentioned. A temperature 
of 55° C. for ten minutes renders innocuous 
the defibrinated blood of the infected ; according to 
the French Commission (Marchoux, Salimbeni 
and Simond) the virus is destroyed in five minutes 
at this temperature. The latter also found that 
defibrinated blood when sealed under vaselin re- 
tained its virulence for five, but not for eight days. 



PROPHYLAXIS. 



719 



The toxic substance appears to have a strong af- 
finity for the parenchymatous organs, particularly 
the liver and kidney. 

The essential principles of prophylaxis have Propiiyiaxis. 
been alluded to: 1, the destruction of breeding 
places for the mosquito as described in the section 
on malaria; 2, the isolation of patients, screened, 
to exclude mosquitoes; 3, the destruction of mos- 
quitoes found in infected houses or ships; 4, the 
individual factor of avoiding the bites of mos- 
quitoes, which involves the screening of houses, 
and individual care. One may go about more 
safely in the middle of the day than before 9 a. 
m. and after 3 p. m. For the disinfection of 
houses, i. e., for the destruction of mosquitoes, two 
pounds of tobacco or two pounds of pyrethrum 
powder per 1,000 cubic feet of space may be burned 
after the rooms are sealed. When smaller quan- 
tities are used the insects may be ..only stupified, 
and should be collected and burned (Rosenau, Par- 
ker, Beyer and Pothier). Sulphur dioxid is highly 
efficient, but formaldehyd is valueless as an in- 
secticide (Posenau). 

The negro is less susceptible to yellow fever than 
the white man and in him the mortality is lower. 
Among the natives the mortality is from 7 to 10 
per cent., among the whites from 20 to 80 per cent. 
(Scheube). The statement that Caucasians may 
become "acclimated" so that they are. less suscep- 
tible needs additional investigation. It seems im- 
possible that acclimatization could mean anything 
else than active immunization. Children and the 
aged are attacked less frequently than those be- 
tween the ages of ten and thirty. 

An attack of yellow fever, whether experimental 
or natural, confers immunity of long or lasting du- 



Suscepti- 
bility. 



720 / \i i:< 1 1<>\ i \/> / 1/ \u a// ) . 

liiiniuiiiiy ration. According to the French Commission, a 

Properties! eortam degree of immunity could be conferred by 

the injection of infected serum which had been 

heated to 55° C. for five minutes, or of defibri- 

nated blood which had been kept under vaselin 
oil at room temperature for eight days. They also 
claimed that the serum of convalescents has pro- 
phylactic and curative properties to a certain de- 

III. "spotted fever" of the rocky mountain 

STATES. 

In the valley of the Bitter Koot River of Mon- 
tana, and in certain sections of Idaho, Wyoming 
and Washington an acute febrile disease, known 
in these localities as spoiled fever, is encountered 
in the month- of spring. The disease Is defined by 
Maxey as '"an acute, endemic, non-contagious, but 
probably infectious, febrile disease, characterized 
clinically by a continuous moderately high fever, 
severe arthritic and muscular pains, and a pro- 
fuse petechial or purpural eruption in the skin, 
appearing first on the ankles, wrists and forehead, 
hut rapidly spreading to all parts of the body." 

In 1902-03, Wilson and Chowning studied many 
cases of the disease in Montana, and described as 
the cause a protozoon organism which they con- 
sider as a piroplasma (Piroplasma homims). The 
organism is a hematozoon, occurring within the 
erythrocytes. Young cells resemble the "hyaline 
bodies" of malaria, are of ovoid shape, 1 micron 
thick and 1 to 2 microns long, and usually occur in 
pairs, but sometimes in numbers of 4 to 16, within 
an erythrocyte. The smaller ends of pairs often 
are directed toward each other, and they may be 



SPOTTED FEVER. 721 

connected by a fine filament. They occur both in 
the red corpuscles and in the plasma. As they 
grow larger, two to three by three to five microns, 
only one parasite usually is found within an ery- 
throcyte, and in this stage they show active ame- 
boid movement with the formation of pseudopodia. 
Eventually they assume a spherical form in fresh 
preparations. They were able to transfer the in- 
fection to rabbits by the inoculation of infected 
blood. 

After identifying the organism as a piroplasma 
and having in mind the part that ticks play in the 
transmission of Texas fever, and perhaps piroplas- 
mosis in other animals (horse, sheep, dog), Wilson 
and Chowning directed their attention to the ques- 
tion of tick bites in those who become infected. 
It developed that of the twenty-three cases exam- 
ined in 1903 all had been bitten by ticks, and 
fourteen had been bitten in from two to eight 
days before the onset of the disease. They con- 
cluded that the disease is transmitted in this 
manner. 

They also searched for some other host than 
man, in which the parasites might flourish contin- 
uously and constitute a source of infection for the 
ticks. This they believe was found in a certain 
gopher (Spermophilus columbianus) . On the west 
side of the river — that side in which the disease 
attacks man — they found the erythrocytes of about 
20 per cent, of the gophers infected with a parasite 
similar to that found in man. On the other hand, 
the blood of sixty-two gophers from the uninfected 
side of the river showed no parasites. "Early in 
the spring the spermophile is said to harbor great 



V n i iii:i I ». 



722 INFECTION AND IMMl MI V. 

numbers of ticks." Similar parasites were found 
in no other Bpecies of animals. 

Stiles, in later investigations, could not confirm 

the results of Wilson and Chowning, being unable 

cither to find the parasites which they described in 

man. or to accept the tick-gopher hypotl 

infectivenesa McCalla and Brereton infected two individuals 

for >Ian ana 

other successively by the bite of a tick which they had 
removed from one of their patients. 

I; kette and his collaborators haw shown thai 
spotted fever can be reproduced with great con- 
Btancy in the guinea-pig by the injection of in- 

!•! 1 or the organs or eggs of infected 

ticks. The Bymptoms of Bpotted fever in the 
guinea-pig appear after an incubation period of 
from two to five days. There is a sudden rise in 
temperature to L05 or L06 1'.. with a general- 
ized roseolaT eruption. Swelling and hemorrhage 
of the scrotum or vulva occurs. The symptoms are 
diagnostic when they occur typically. The mon- 
key, rabbit, horse and at leasi fivi species of small 
wild animals have a greater or less degree of sus- 
ceptibility. 

Ricketts and King, working independently, were 
able to transmit spotted fever from diseased to 
normal guinea-pigs by allowing ticks which had 
fed on diseased pigs to bite normal pigs. Bicketts 
and Wilder were able to show that up to 50 per 
cent, of infected ticks transmitted the infection to 
their young. It was found that nymphs develop- 
ing from infected larvae were infectious for guinea- 
pigs, and that in a similar way adult ticks devel- 
oping from nymphs were able to transmit spotted 
fever. Xaturallv infected ticks were discoveerd in 



SPOTTED FEVER. 723 

1907. In order to ascertain the probable source 
of the virus as occurring in the tick, Eicketts 
showed that ground squirrels, rock squirrels, chip- 
munks and ground-hogs were susceptible to the 
disease. 

Eicketts concludes as follows as to the mainte- Maintenance. 
nance of spotted fever: "In accordance with the 
results and deductions which have been outlined, 
it is conceived that spotted fever is maintained as 
follows : A certain percentage of the female ticks 
which have acquired the disease as a consequence 
of feeding on animals, the latter having been in- 
fected by other ticks, transmit the disease to their 
offspring through the egg. The new generation, 
during the process of feeding, transfer the virus 
to certain of the susceptible small wild animals 
(ground squirrels, rock squirrels, chipmunks, 
ground hogs, and perhaps others), and this may 
take place during either the larval, nymphal or 
adult stage, hence at various times of the year. 
During the infection of the wild animal it is re- 
quired that hitherto normal ticks, either as larvae, 
nymphs or adults, acquire the disease by feeding 
simultaneously with, or shortly after, the feeding 
of the infected ticks. Eegardless of the tick's 
stage of development at the time it acquired the 
disease, the virus is retained into the adult period, 
and in certain of the females reaches the germ 
cells and again appears in the next generation. 
The infection of man is an unessential incident 
for maintenance, and depends on the occasional 
and accidental bite of the infected adult tick." 

The virus of spotted fever is not filterable 
through Berkefeld candles. The eggs of infec- 



724 INFECTION AND IMMUNITY. 

HieroMe tious ticks were found by Ricketts to contain a 
Ktioiour>. | ;ii .^. (i Iiuill | )( . r | slna ii polar Btaining bacilli, 

These organisms were agglutinated in high dilu- 
fcioD by tlif Berum of Bpotted Gever cases, l >ut are 
found in the eggs of Don-virulent ticks. At- 
tempts at cultivation by Ricketts and Beinemann 
haw been negative. 

Immunity. \n authoritative IVpurt of B S«vnnd attack of 

Bpotted fever is on record. According to Ricketts 
an<l Gomez, an attack of Bpotted fever in the 
guinea-pig and monkey produces a Btrong active 
immunity of long duration. This immunity is 
characterized by the presence of protective anti- 
bodies in the Berum which may be demonstrated 
by injecting mixtures of virus and immune serum. 
I concentration of the antibodies in the blood 
of the immune animal undergoes ;i decrease in the 
course of Beveral w< 

The female that has recovered from Bpotted 
fever transmits immunity to her young. The 
young are immune even when the female acquired 
her immunity Beveral months before impregna- 
tion. The immunity of the young does not de- 
pend on the ingestion <>!' milk from the immune 
mother. The character of the inherited immunity 
has not yet been determined, although it is pre- 
sumptively a passive immunity that differs from 
the }>a>>iw immunity conferred by the injection 
of immune serum by its longer duration. The 
long duration of the inherited immunity may 
depend on the longer time required for the elimi- 
nation of large quantities of protective substances. 

Passive immunity may be established in the 
healthy guinea-pig by the injection of blood or 



TYPHUS FEVER. 



725 



serum from the immune guinea-pig. The immune 
defibrinated blood contains antibodies in such con- 
centration that 0.1 c. c. often protects against 1 
c. c. of third-day virus, representing anywhere 
from 30 to 100 minimum pathogenic doses. In 
other instances 0.3 or 0.4 c, c. of immune blood 
are required for this degree of protection. When 
1 c. c. of strong immune blood is injected subcu- 
taneously into healthy guinea-pigs, the passive 
immunity is still present in marked degree after 
twenty days; after thirty -eight days it is present 
only in such degree that a mild course of spotted 
fever results when virus is injected; after forty- 
five days it is no longer manifest. It is possible 
that passive immunity would not last so long if 
the immune blood is injected into a foreign 
species. 

The guinea-pig may be protected against spotted 
fever following its inoculation with infected blood, 
provided the immune blood is administered on 
the second or third day after inoculation. 

The work of Eicketts indicates that efforts at 
prophylaxis are to be directed toward the exter- 
mination of ticks and the wild animals which 
harbor them. 

Serotherapy will probably depend on the culti- 
vation of the microbic cause of the disease. 



Prophylaxis 
and Sero- 
therapy. 



IV. TYPHUS FEVER. 

Typhus is now a rare disease. It is endemic on occurrence 
a small scale in London, Glasgow and Liverpool, g?ousnes*~ 
and cases occur in the larger cities of Ireland. In 
epidemic form it attacks localities in which the 
hygienic conditions are bad. The contagion seems 



726 INFECTION AND IUUI Mi V. 

asten itself in such localities and does not ex* 
tend with rapidity to neighboring communities in 
which good hygiene and cleanliness prevail; it is 
particularly a disease of the poor, the filthy and 

the underfed. Healthy, clean and well-nour- 
I persons who enter an infected district and 
come in coin act with the patients are suhject to 
attack. Typhus has always been considered a very 
contagioi It has been noted repeatedly, 

that when patients are removed to a hos- 
pital and kept under clean and hygienic conditions 
with plenty of fresh air that infection of attend- 
ants and physicians is relatively infrequent. 
Mexican typhus, or tabardilli, resembles Euro- 
typhus closely, hut lias a longer inciihalioii 

iod and rei sis a few days before 

European t\ phue doi s. There is less tendency 
t.> confluent eruption and hemorrhage. 
Pathoire- Nicolle and his i - were able to produce 

"Vi!imni* r typhus in the chimpanzee by the injection of 
blood from European typhus patients and in a 
similar way in the Afacacua monkey with blood 
from infected chimpanzees. Direct transmission 
from man to the macacua was not accomplished. 
Anderson and Goldberger were aide to transmit 
tahardillo directly to the monkey by inoculations 
with the blood of typhus patients. Their results 
were confirmed by Ricketts and Wilder, who deter- 
mined the following points: "1. Macacus rhesis 
can be infected with tabardillo invariably by the 
injection of virulent blood from man taken on 
the eighth to tenth day of fever. 2. Attempts to 
maintain typhus in the monkey by passage through 
other monkeys were unsuccessful. 3. Monkeys 



TYPHUS FEVER. 727 

niay pass through an attack of typhus so mild 
that it can not be recognized clinically. Vaccina- 
tion results." 

Mcolle succeeded in transmitting the typhus Transmission. 
fever of Tunis from chimpanzees to monkeys by 
means of the common body louse. Anderson and 
Goldberger and Eicketts and Wilder succeeded in 
producing tabardillo in the monkey through the 
bite of the louse. The lice were allowed to feed 
on the blood of patients with tabardillo and sub- 
sequently permitted to bite the monkeys. Eicketts 
and Wilder also demonstrated that infected lice 
transmitted the infection to their eggs, which gave 
rise to lice capable of infecting monkeys. Their 
observations of the spread of the disease render it 
reasonably certain that lice are the ordinary means 
of transmission. Studies on the bed bug and flea 
indicate that they play no part in the spread of 
this infection. 

The virus of typhus fever is not filterable. 3iicroMc 
Various organisms have been described in the 
blood. Eicketts and Wilder describe a small bac- 
illus in stained blood preparations. The organism 
resembles the plague bacillus and those organisms 
described in spotted fever. The organism was 
also found in the intestinal tract of infected lice. 
Cultivation was unsuccessful. Further studies 
are necessary to establish the etiologic relation- 
ship to typhus. 

The production of immunity through a light immunity. 
attack of typhus in the monkey has already been 
mentioned. The serum of convalescents is said to 
be curative in a moderate degree (Legrain). 



7_'^ INFECTION AM> IMMUNITY. 

v. DENGUE fevi:;:. 

Dengue occura in numerous countries which af- 
ford a warm climate. It i> endemic in Egypt, 
Arabia, Senegambia, Honduras, the Bermudas, 
and the Sandwich Islands. Important centers for 
the origin of epidemics are the Less* c Antilles of 
the Western Hemisphere, the Red Sea Coast, 
and Senegambia (de Brim, cited by Scheube). It 
occurs in our southern states and In Mexico. It 
may be introduced into new regions by means of 
ited ships. 

"Dengue fever is an acute infectious disease, 
distinguished by the appearance of an initial and 
terminal polymorphous eruption and accompanied 
articular and muscular pains." Corre- 
Bponding with the two eruptions, there are charac- 
teristically two periods of temperature separated 
by a short period of apyrexia. The intense muscu- 
lar pains and asthenia resemble those of influenza, 
the t factions of the latter being absent, 

however. The incubation period varies from a few 
hours to four or five days, usually one or two, and 
the entire duration from six to seven days. 
TammsmiMioa. Eberle, in 1904, advanced the hypothesis that 
_:;•• is transmitted by a mosquito (Culex fati- 
gans). He described a "plasmeba" in the blood 
of patients with the disease. Other observers have 
failed to find protozoa in the blood. Ashburn and 
Craig (1007) were able to transmit the disease to 
healthy men by injecting the blood of infected 
individuals. They were able to produce the dis- 
ease by allowing mosquitoes, which had fed on 
dengue patients, to bite healthy men. Their 
studies also showed that the distribution of the 
Culex fatagans corresponded with that of dengue, 



ACUTE ARTICULAR RHEUMATISM. 



729 



thus putting the hypothesis of Eberle on a firm 
basis. 

Ashburn and Craig were unable to find the or- 
ganism responsible for the disease, but demon- 
strated that the filtered blood of infected persons 
can produce the disease in healthy subjects. They 
were unable to cultivate or detect in other ways 
any micro-organisms. 

According to Ashburn and Craig, an attack of 
dengue confers immunity. They were unable to 
produce a second attack by the injection of infec- 
tious blood in individuals who had recovered from 
the disease. 



Filterability 
of Virus. 



VI. ACUTE ARTICULAR RHEUMATISM. 

(See p. 525.) 

VII. SMALLPOX AND VACCINIA. 

Vaccinia and smallpox may be considered to- Relation of 

gether, having in mind the likelihood or, indeed, smallpox, 
the certainty, that they have a common etiology. 
This view seems the only possible one, in spite of 
our uncertainty as to the exact nature of the cause. 
To hold a different view would be to acknowledge 
that immunization with one kind of microbe may 
confer immunity of the strongest and most spe- 
cific character against another, a condition for 
which we could find no parallel. 

More satisfactory knowledge, however, comes j££ c caif io ^itH 
from actual conversion of smallpox virus into vac- smallpox. 
cine virus by passing the former through cows. 
Abbot quotes W. J. Simpson as follows : "In No- 
vember, 1885, with smallpox lymph from an un- 
vaccinated patient, ] inoculated a cow with fifth- 
day lymph and a ewe with eight-day lymph from 



780 INFECTION AND IMMUNITY, 

the same patient. Both presented vesicles on the 
seventh day, the lymph of which I sent to London 
to be used by Dr. Cory, the director of the Animal 
Vaccine Institute of London. This calf lymph, 
which Dr. Cory passed through a second calf before 
using it on children, was the starting point of a 
new vaccine at the institute. Between Nov. 21, 
1885, and May 6, 1886, 1,247 children had been 
vaccinated with this Lymph and gave 98.4 per 
cent, insertions of success." 

Concerning the changes which smallpox virus 
undergoes in the cow, as a result of which it loses 
permanently the power of causing smallpox in 
man, we have no knowledge, aside from the hy- 
pothesis of Councilman and others mentioned below. 

We may pass over the various bacilli and cocci 
which have been described as causing vaccinia and 
smallpox with the remark that none of them are 
of primary significance, but that they have been 
either accidental contaminations or the causes of 
secondary infections during the course of the dis- 
ease. 

There are two chief theories as to the cause of 
smallpox (and vaccinia) to-day. One, that the virus 
is an ultra-microscopic and uncultivatable organ- 
ism ; and a second, that it is represented by certain 
protozoon-like bodies seen in the specific lesions 
(vesicles, pustules) of both vaccinia and smallpox. 
Concerning the first theory we know nothing be- 
yond the observation of Parke that the virus of both 
vaccinia and variola did not pass through Berke- 
feld and Chamberland filters under the conditions 
of his experiments. Of the second theory a brief 
review may be given. 



CYTORYCTES VARIOLA. 



731 



Protozoon-like bodies have been seen by many 
observers and were first brought into causal rela- 
tion with smallpox by Van der Loefi 3 and by L. 
Pfieffer (1887). Guarnieri (1892), however, gave 
the subject its present impetus by a careful study 
of these forms as seen in vaccinia and gave to the 
hypothetical organism the name of Cytoryctes vac- 
cinia, s. variola?. The bodies were found within 
the deep epithelial cells in the pustules of vaccinia 
and smallpox and in the lesions produced on the 
cornea of the rabbit by inoculation with the viruses 
of vaccinia and smallpox. They lie within clear 
spaces in the protoplasm of the cells, vary in size 
from that of a micrococcus to that of an epithelial 
nucleus and multiply, it was supposed, by binary 
division. When mounted in hanging-drops of the 
vesicular fluid they showed ameboid movements. 
Confirmatory work came from others, and partic- 
ularly Wasielewski, who concluded that the "vac- 
cine bodies" are perfectly characteristic, that they 
are never found in normal or other pathological 
conditions of the skin, that they can not originate 
from leucocytes or epithelial cells, and hence can 
not be accidental "cell inclusions." Filtered virus 
produced no lesions in the cornea of the rabbit. 

Eecently Councilman, Magrath and Brincker- 
hoff have studied this supposed organism in great 
detail and find, in addition to the forms in the cy- 
toplasm (cytoplasmic parasites), still others within 
the nucleus of the epithelial cells of the vesicles 
and pustules. They express the belief that the or- 
ganism first gains entrance to the cytoplasm of the 
cells, and after a period of "multiplicative prolif- 
eration," the products of the latter process pene- 
trate the nuclei of the epithelial cells and there 



Cytoryctes 
Variola, a 

Protozoon. (?) 



Work of 

Councilman 
and Others. 



732 INFECTION AND 1M \n Ml ). 

undergo another type of proliferation. Calkins, 
the zoologist, after Btudying the material, Bharea 

their views and has constructed a life cycle of the 
parasite from the various forms which he found in 
fixed and stained preparations. 

Lite History The Binallest recognizable forma in the cytoplasm 
► i Oytorretea. measure about u.7 of a microo and lie in a vacuole in 

the cytoplasm near the nucleus. Calkins interprets 
these as "gemmules" and as products of the prolifera- 
tion o! Lhe parasite at the primary point of in; 
(lunga (T) ). Somewhat larger forma (3 microns) con- 
taining a vacuole with B central point staining with 
. methylene blue, represent "gemmules" which have grown 

ami have become somewhat differentiated. The periphery 
of the organism becomes differentiated also by the for- 
mat ion of minute dots which may eventually be stained 
by a Bpecia] method. During this Btage the organism 
•piaamic "often is Bpherical, but may be fusiform, pyriform or 
ameboid, while pseudopodia are frequently caught in 
various degrees of extension." No definite nucleus is 
discernible, but material corresponding to nuclear sub- 
Btance is distributed Bomewhat generally through the 
parasitic cell. Certain granules are distributed through- 
out the body of the organism, and these granules eventu- 
ally give rise to the "gemmules" or young parasites 
which become free by the disintegration of the mother 
cell. 

Howard and Perkins find, in addition to the cyto- 
plasmic Btage of Councilman and his co-workers, a sec- 
ond cytoplasmic stage, the products of which penetrate 
the nucleus to institute the intranuclear stages. Cal- 
kins speaks of the fate of the gemmules as follows: 
"The germs formed by the multiplicative reproduction 
of the cytoplasmic ameboid form of the parasite may 
develop into new cytoplasmic organisms or ultimately 
may become germ cells within the nucleus of the epithe- 
lial cell. In the latter case they develop into struc- 
tures which I regard as gametocytes. The resulting 
zygote (formed by conjugation of the gametes) is the 
ameboid pansporoblast mother organism." 



Staarea. 



GYTORYCTES VARIOLA. 



733 



The conclusion that conjugation takes place is based Xuclear 
on certain analogies with other micro-organisms, rather a sres. 
than on observation of the phenomenon. This intra- 
nuclear mother organism, the product of conjugation, 
finally grows to a size of 10 to 12 microns and forms 
within it from eight to twenty "primary sporoblasts." 
The young sporoblasts are eventually liberated from the 
mother cell and are at first solid and homogeneous, like 
the gemmules, but later when they have reached a size of 
iy s to 2 microns small vacuoles appear in the peripheral 
ring of substance and in each vacuole a young spore is 
formed. The formation of these spores terminates the 
"primary nuclear phase" of the organism. These spores, 
still within the nucleus of the epithelial cell, become, 
in their turn, sporoblasts, and the formation of a large 
number of secondary spores within them constitutes the 
secondary nuclear phase of a parasite. In the mean- 
time the nucleus of the epithelial cell has degenerated, 
and the secondary sporoblast with its contained spores 
escapes first into the cytoplasm and eventually into the 
pericellular space. In accordance with this conception 
the intranuclear process is well calculated to give rise 
to a massive number of young parasites within the body. 
Councilman, Magrath and Brinckerhoff state that after 
the tenth day of the disease the parasites become more 
and more difficult of recognition by microscopic methods. 
However, Brinckerhoff found that even the desiccated 
crusts of pustules and vesicles produce typical lesions 
on the cornea of the rabbit. These forms have never 
been recognized positively in the blood of patients, and 
Magrath and Brinckerhoff were not able to produce le- 
sions in the rabbit's cornea by inoculation of variolous 
blood. The general distribution of the lesions in the 
skin and the occurrence of fetal smallpox gives us abun- 
dant reason for believing that the blood stream is in- 
vaded by the parasites. 

It was stated above that bodies of the general nature cytoi-ycetes 
of those described are found in vaccinia as well as in in Vaccinia. 
smallpox, and this occurrence is some added reason for 
believing that Gytoryctes variolas, s. vaccinice, is the 
cause of these processes. It is a most interesting and 
important observation by the American authors cited 



734 INFECTION AND IMMUNITY, 

that the intranuclear stage of the parasite does not 
occur in vaccinia (Tyzzer), and we are led to believe 
that this is an important differentia] point between 
vaccinia and smallpox. Assuming that the bodies in 
question cause the disease, the thought is pertinent that 
the dilTerence in virulence between vaccinia and variola 
inoculata may depend on the failure of the intranuclear 
cycle to appear in vaccinia. 

The work of Guarnieri, and particularly that oi 
Councilman, Magrath and Brinckerhoff, is most 
~ii\v. and ardent supporters of their views 
have appeared with corroborative work (e. g., How- 
ard). At the same time many skilled observers 
■ lit entirely the parasitic- nature of the bodies 
ibedj interpreting them rather as products 
pithelial cells and nuclei 
or as inclusions of other tissue cells (e. g., leuco- 
r fragments of other nuclei. Ewing 
expresses similar views. The state of the question 
is such that further study is urgently called for. 
infection We have no positive knowledge as to infection 
atrium in smallpox, although the existence of a 
"contagious zone" of atmosphere about the patients 
is good ground for the belief that invasion takes 
place through the respiratory passages. The disease 
which follows introduction of the virus into the 
skin is spoken of as variola inoculata, and is much 
less severe than smallpox. We are also ignorant to 
a large degree of the means of excretion or dissem- 
mination of the virus. Osier states that the virus 
Disseminm- "exists in the secretions and excretions and in the 
exhalations from the lungs and skin." The dried 
epithelial cells which are continuously thrown off 
are no doubt a most important means of dissemina- 
tion. Infection may be transmitted by means of 
clothing or other materials which have been in con- 



At r i 11 i.i. 



tion. 



GY TORY GTE 8 VARIOLA. 



735 



tact with patients, and the disease may be carried 
to others from the sickroom by a healthy person. 
Epidemiologic experience teaches that the vims is 
one of great resistance and tenacity. 

The incubation period in variola falls within the cyclic 
extremes of eight to twenty days, most commonly symptoms. 
from nine to fifteen days. The stage of invasion, 
or the primary fever, terminates the incubation 
period, and during this time the initial rash ap- 
pears, accompanied by moderate hyperleucocytosis. 
On the third to the fourth days the remission sets 
in, the number of leucocytes in the blood decreases 
to normal or below normal, and cutaneous lesions 
make their appearance, and in the course of forty- 
eight hours show a vesicular nature. When the 
umbilicated vesicles are changed into pustules the 
temperature again rises (secondary fever) and hy- 
perleucocytosis again develops. This much only 
of the clinical picture is mentioned to emphasize 
the cyclic nature of the phenomena ; one may well 
suspect that the organism causing such a disease 
undergoes particular phases of development which 
in some way are related to the well-known clinical 
cycle. 

Epidemics are sometimes of so mild a charac- variations 
ter that the patients are not bed-ridden and may lnVirnlence - 
be found in the pursuit of their occupations in 
spite of well-marked eruptions. Such occurrences 
can be referred only to a virus of low pathogeni- 
city. Even mild epidemics, however, may be ac- 
companied by severe and fatal cases. Cases of am- 
bulatory smallpox are most important factors in 
spreading the disease. 

We have nothing more than presumptive knowl- 
edge concerning the distribution of the virus in 



736 INFECTION IND IMMUNITY. 

Distribution the body aside from its occurrence in the skin and 

Body, mucous membranes. We may fee] certain, how- 

. that the infection is systemic. The lesions 

of the skin are of such a nature that they are 

rally regarded as of embolic character, which 

lood infection; and transmission of 

the disease through the placenta is decisive proof 

of a general distribution of the virus at some stage 

of the process. The failure to cause vaccinia in 

the cornea of the rabbit by inoculating the blood 

of patients (cited above) may indicate that the 

virus is present in the blood in small quantity or 

that circulating organisms are eventually de- 

Btroyed. The intoxication of smallpox is mani- 

aeral. 

v '-' j,i > J ii lVv. secondary infection play so 

Infections. A1 . J , ** » 

important a role as in smallpox. When the cu- 

tan- eiie pustular they usually 

contain pyogenic cocci, although they may be ab- 
aewhat strange that streptococci are 
often encountered than staphylococci, in 
view of the normal presence of the latter in the 
epidermis. Fatal < ilmost without excep- 

tion accompanied by general streptococcus infec- 
tions, and Councilman believes these organisms 
are more important as a cause of death than the 
specific virus. 
Propkyiaxi*. Successful prophylaxis involves universal vac- 
cination, in addition to special measures which are 
demanded in the presence of the disease: isola- 
tion of the sick until desquamation is complete, 
antiseptic baths, and disinfection and fumigation 
as currently practiced. 

Interesting matters of history are the facts that 
protective inoculation against smallpox was prac- 



VACCINATION. 737 

ticed in fairly ancient times by rather primitive Discovery -of 

\ no dilution. 

races, and that Lady Mary Wortley Montague 
introduced this method into Europe in 1718. 
This was not the vaccination in vogue to-day, 
however, but rather the inoculation of virulent 
virus from the pustules of the diseased into the 
healthy. As mentioned in one of the earlier chap- 
ters, this procedure commonly produced a mild 
type of disease (variola inoculata) which ren- 
dered the individual immune to virulent small- 
pox. 

Everyone knows that the vaccination of to-day, .tenner. 
i. e., the substitution of the virus of cowpox for 
that of smallpox, was the discovery of Jenner 
(1798), and we need offer no comments concern- 
ing its efficacy nor repeat the well-earned epithets 
which have been applied to the rare species of dis- 
believers. Nothing is more certain than that 
smallpox has ceased to be a world pest only be- 
cause of the continued Jennerization of the race. 

The essential points established by Jenner are 
the following: 1. That the vaccine disease 
casually communicated to man has the power of 
rendering him insusceptible to smallpox. 2. That 
the specific cowpox alone, and not other eruptions 
affecting the cow which might be confounded with 
it, has this protective power. 3. That the cow- 
pox may be communicated at will from the cow to 
man, by the hand of the surgeon, whenever the 
requisite opportunity exists. 4. That the cowpox, 
once engrafted on the human subject, may be con- 
tinued from individual to individual by successive 
transmissions, conferring on each the same im- 
munity against smallpox as was produced in the 



» III l> ll . 



/.\ / /:< ■■/ m\ i \ D IMMUNITY. 

first Infected directly from the cow (cited 
>m S. W. Abbott). 
;;' For at Least half a century following Jenner*i 
discover)' humanized Lymph was used for vacci- 
nat ion . new patients being inoculated by means 

Dints prepared from I previous 

or with the fresh Lymph from such cases. The not 
infrequent transmission of Byphilis by this means 
was the source of many calamities. Following the 
precedent of Warlemont in 1868, the Lymph of 
cowpox is dow th<' universal source of vaccine. 
,,,x> > ,,,x - Cowpox probably occurs to a or less 

all countries, especially in the spring and 
summer, attacks the adder and teats almost ex- 
clusively, and is accompanied by very mild con- 
stitutional sympton incubation period is 

local 
. swelling and tenderness, followed by the for- 
mation of papules, which in three or four days 
after their appearance are transformed into vesi- 
The disi es its maximum develop- 

ment at the tenth or eleventh day. the umhilicated 
vesicles going through the usual course to crust 
atdon. 
'of vaol-V.u". Calves and heifers from the age of two months 
to two years are best suited for vaccination in the 
production of lymph for commercial purposes. 
The region of the flank or the whole ventral sur- 
face of the body may be inoculated, and in the lat- 
ter instance as many as a hundred or more inser- 
tions may be made. The skin is first shaved, 
cleansed with antiseptics, and the lymph from an- 
other calf is introduced by means of a syringe or 
by scarification. In some institutions long, very 
superficial parallel incisions are made and the 



tion. 



VACCIXATIOX. 739 

virus rubbed in with a spatula. Within from five 
days to a week the vesicles are in such condition 
that the lymph may be collected, the contents 
either being squeezed out with suitably formed 
forceps or scooped out with a sharp spoon. De- 
pending on the area vaccinated, the lymph col- 
lected from a single calf may be sufficient for 
from 2,000 to 15,000 vaccinations in man. Be- 
cause of the immunity which is conferred, calves 
can be used but once for the production of vaccine 
virus. 

All other methods of preserving lymph have Giycer 
been largely abandoned for the process of 
glycerinization, the glycerin being very inti- 
mately mixed with the virus by mechanical 
means and allowed to remain in this state in 
a cool place for from six to eight weeks before 
the product is put on the market. Dried vaccine 
on ivory points is still used to some extent, the 
points being coated directly from the vesicles. 
Dried vaccine retains its power for from two to 
four months or longer when kept in a cool, dark, 
dry place. Glycerinated lymph has many advan- 
tages, the most important of which relates to the Effect on 
bactericidal action of the glycerin by which the ing- Bacteria. 
lymph is freed from the pathogenic bacteria (e. g., 
staphylococci) which in former times caused ser- 
ious complications .in vaccination. The glycerin 
is supposed to destroy such organisms to a large 
degree without, however, injuring the vaccine 
virus itself. It is also stated that glycerinated 
lymph is much more durable than the dried ; that 
its potency may be retained for eight months or 
longer under suitable conditions. Rosenau has 
recently called attention to the fact that the bac- 



7 in / \ r/ri ln\ \\ I) I \l \ll Ml). 

tericidal power of glycerin has been overestimated, 
and that while it kills pyogenic cocci within two 
weeks when at the body temperature, such organ- 
isms may live for months in glycerin when in the 
ice chesi ; and, of course, our glycerinated virus 
is kept in the ire chest. Tetanus spores live for 
months in glycerin and glycerin has practically 
no neutralizing action on tetanus toxin. Glycerin 
does have the power, however, of attenuating the 
tetanus Bpores, ami its slow bactericidal action is 
well established. As stated above, the vaccine 

should he glycerinized for some weeks hefore it is 
put <m the market. Glycerin has the added ad- 
vantage for the manufacturer of enabling him to 

dilute his lymph moderately (from 50 to <»<» per 
cent, i \\ ithniit impairing the virus. 

Of much more importance for the safety of 
vims than glycerinization are proper hygiene and 
cleanliness during the whole process of prepara- 
tion. The powers recently '(inferred on the Sur- 
geon-General by an act of Congress have resulted 
in a great improvement in the purity of the vac- 
cina m»w on the market. 1 

While it can Dot be expected that vaccine will 
be entirely free from bacteria, it is possible to re- 
duce their number to a low minimum and to elim- 
inate pathogenic forms, particularly pathogenic 
cocci, tetanus and tubercle bacilli. 
vncciimtion. The teehnic of vaccination is so well known 
that no description is needed. It need only be 
stated that in scarifying it is undesirable to. 
cause hemorrhage and that the operation is a sur- 
gical procedure, demanding surgical cleanliness 

1. John F. Anderson "Federal Control of Vaccine Virus," 
Jour, of the Amer. Med. Assn.. June 10. 1905. 



VACCINATION. 741 

and surgical care of the wound. As a rule vac- 
cination in man protects against smallpox for a 
period of six to ten years, after which revaccina- 
tion is necessary for continued protection. It 
should not be concluded from the negative out- 
come of a single vaccination that the individual is 
immune to vaccination and hence immune to 
smallpox, but rather, repeated attempts should be 
made with virus known to be fresh. It is quite 
possible that certain individuals are immune to 
vaccinia, as often stated, but they are very rare, 
and the condition should not be recognized nastily. 
Among 38,000 vaccinations Dr. Cory encountered 
but one in which a "take" could not be obtained 
on second trial (Abbott). 

The ideal condition is that all children should P e " to 

• i • p Vaccinate. 

be vaccinated at an early age by requirement of 
law as in certain European countries, where it is 
demanded within the first few months or the first 
year or two of life. Some countries require re- 
vaccination before the children are admitted to 
school and recommend repetitions at suitable in- * 
tervals. 

We have no national law on the subject and the 
state laws differ. In many states children must 
be vaccinated before they are admitted to the pub- 
lic schools, the responsibility sometimes falling 
on the school and sometimes on the city or town 
authorities. A number of states have no laws on 
the subject, although vaccination is for the most 
part assured through the requirements of the 
state boards of health and the local authorities. 

When there is danger of an epidemic, and in 
known cases of exposure, vaccination should be 
practiced thoroughly. Inasmuch as the incuba- 



..I B«a< 



742 / \ FECTlOy \ \ l> IMMUNITY. 

won period of vaccinia Is about three days less 
than that of smallpox, successful vaccination pro- 
tects within a Limited period following exposure. 
Immediate vaccination is demanded in ease of 
exposure. Healthy infants may be vaccinated 
within the iirst six weeks or two months of life 
ami at any earlier period in case of exposure. 

An attack of smallpox confers prolonged and, 
tii.mty. with few exceptions, lasting immunity. Second 
and even third attacks have keen described. It is 
known that those who have had smallpox may be- 
come susceptible to vaccination after a period of 
t i in* . Sui ' ibility varies a good deal wit 
During the ages of from two to fourteen years 
the diseai common than between fifteen 

and forty, aid after this period it again de< i 
in frequency. Undoubted instances of natural 
immunity to smallpox occur, hut they are very 
rare. 
eocyte«. >., : . companied h\ a leucocytosis 

which is peculiar because of the large number of 
mononuclears. There is a slighl rise in the 
Dumber of leucocytes during the first febrile on- 
B fall to almost normal during the remission, 
followed by a second rise, which may be as high 
as 16,000 to 20,000. Fatal eases show a terminal 
hypoleucocytosis (Magrath, Brinekerhoff and Ban- 
croft). Large numbers of lymphocytes are also 
found in the pustules (Eoger). Nothing of a sat- 
isfactory nature is known concerning the relation- 
ship of the leucocytes to recovery and immunity. 
serum. There is no serum therapy for smallpox. The 
interesting observation has been made, however, 
that the serum of convalescents or of vaccinated 



VARICELLA. 743 

man or animal will, when mixed with vaccine 
virus, prevent its action. 

Horsepox is identical with cowpox. Sheeppox 
(clavel^e) is an independent disease. The virus of cow- 
pox produces a local lesion in the sheep, but does not 
cause immunity to sheeppox. The virus of sheeppox, on 
the other hand, has no effect on horses and cattle 
(Nbcard and Leclainche). The virus of sheeppox is 
filterable (Borrel). 

VIII. CHICKENPOX (VARICELLA). 

Although the skin manifestations of varicella 
often resemble those of smallpox to such an 
extent that differentiation is difficult, the two 
diseases are distinct. Nothing indicates this more 
clearly than the fact that one who has recovered 
from varicella is susceptible to vaccination, and it 
is known further that an attack of chickenpox 
does not protect against smallpox. 

The etiology is unknown, and no organism 
which has been described can be considered the 
probable cause. 

Varicella occurs epidemically and sporadically. 
The virus probably exists in the lesions of the 
skin and in the scales, and the latter may be the 
chief source of contagion. There is no definite 
knowledge concerning the resistance of the virus, 
nor its distribution; the conclusion is justified, 
however, that it exists in the circulation at least 
in an early stage of the disease. The infection 
atrium likewise is a matter of conjecture, but 
probably is to be found in the lungs or upper 
respirator}^ tract. 

The patients should be isolated and school chil- 
dren should not be allowed to return to school 



:n / \ i I :<■ 1 1<>\ i \ /> / 1/ 1// \// ) . 

until desquamation is complete. Disinfection 
should Ik 1 practiced. 

Susceptibility and virulence would seem to vary, 
-inc.- the severity of the cutaneous lesions is doI 
constant. In delicate and tuberculous children. 
the lesions may become gangrenous. Eemorrhagic 
varicella is observed occasionally. Such compii- 
cations as nephritis and otitis media occur. 

Varicella is a disease of childhood, although it 
may occur in adults. Infants are attacked less 
frequently. Si ad or even third attacks occur, 
although they are rare. 

The:. rotherapy. 

! v. 3CABLEI FEVER. 

The r61e which the streptococcus plays in scarlet 
was consider* d on page 521 . 

lies" recently observed by Mallory may 
i briefly. 
Mi*- Proto- In 1903 Mallory described certain protozoon- 
" M£ilory. like bodies found in the skin of four cases. They 
could be divided into two groups, one of which 
consisted of "round, oval, elongated, lobulated 
bodies" from 2 to 7 microns in diameter; the indi- 
viduals of the second group "contain a central 
round body, around which are grouped, on optical 
ion, from 10 to 18 narrow segments, which, in 
some cases, are united, but in others are sharply 
separated laterally from each other." They occur 
within and between the epithelial cells and in the 
superficial part of the corium. He gives the name 
of Cyclastcr scarlatinalis to these bodies, and, al- 
though expressing the belief that they are protozoa 
and have a causal relation to scarlet fever, does not 
claim to have proved such a relation. 






SCARLET FEVER. 



745 



Contagious- 
ness and 
Transmission. 



Duval corroborated the discovery of Mallory, 
and demonstrated the bodies in five out of eighteen 
cases in blisters which were produced artificially 
during the height of the eruption. Field found 
them not only in the skin of scarlet fever, but also 
in that of measles and concludes that many of 
them at least represent artifacts or degeneration 
forms of tissue cells. More extensive observations 
seem to be necessary to establish the nature of 
these supposed parasites. 

Other micro-organisms which have been de- 
scribed as the cause of scarlet fever, including the 
Diplococcus scarlatina of Class, we may pass over 
with the remark that the claims concerning them 
have not been upheld. 

The contagiousness of scarlet fever is extreme, 
and the virus undoubtedly is thrown into the sur- 
rounding air from the skin of the patient. It is 
highly probable that the virus also reaches the sur- 
rounding air from the respiratory passages ' by 
means of "drop infection," since transmission may 
occur before the skin shows involvement. Patients 
continue to be infectious for from 4 to 6 weeks or 
longer after the appearance of the eruption. The 
disease may be transmitted by an intermediate 
healthy person, or by contaminated clothing or 
furnishings. The origin of epidemics from milk 
which has in some way been contaminated seems 
to have been proved in a number of instances. 

Of great importance for the persistence of an 
epidemic is the resistance of the virus, which re- 
mains viable and virulent for months and possibly 
for years, when under suitable conditions. 

Prophylaxis demands isolation of the patients Prophylaxis. 
until desquamation is complete; the use of anti- 



74(1 / \ FECTIO \ A \ /> l M Ml S 11 ) . 

septic bathe or ointments, or vigorous scrubbing 
with soap as desquamation proceeds: antiseptic 
treatment of the month cavity; disinfection o[ all 
utensils, linen, etc., with which the patient has 
hern in contact ; avoidance of stirring up the dust 
in the room, which demands moist rather than dry 
cleansing; the disinfection of the sputum and 
other discharges of the patient; an abundance of 
air and sunshine in the sick room; the final 
disinfection of the room. Physicians ami nurses, 
when in the presence of the patient, should wear 
long gowns, which can he discarded on leaving, 
and other well-known precautions should be ob- 
served to avoid spreading of the disease. The pro- 
phylactic vaccination by mean- of streptococcus 
(Gabritchew8ky) i- deserving of further trial. 
Suseeptl- Scarlet fevei is particularly a disease of child- 
iiiiiiiniiio. hood, "a large proportion of cases occurring before 
the i' " (Osier). Adults are attacked not 

infrequently. Infants are less susceptible than 
older children. Many examples of family immun- 
ity, which probably is relative, are encountered, 
and likewise instances in which there is a family 
susceptibility. In a given family examples of in- 
dividual immunity and susceptibility are fre- 
quently met with. One attack usually confers im- 
munity against a second, but not invariably. 
Leucocytes. Scarlatina is characterized by a leucocytosis, 
the degree of which bears some relation to the 
severity of the infection. In mild cases the aver- 
age is from 10,000 to 18,850 (Bowie), in moder- 
ately severe eases from 20,000 to 40,000, or even as 
high as 78,000 (Klotz) ; in malignant uncompli- 
cated cases there is a tendency to a low leucocyte- 



MEASLES. 



747 



sis (Klotz). How much of this leucocytosis de- 
pends on co-existing streptococcus infection re- 
mains uncertain. 

Treatment with antistreptococcus serum is the 
only serotherapeutic measure which has been ad- 
vocated in relation to scarlet fever. This is done 
either on the assumption that the disease is of 
streptococcus etiology, satisfactory proof of which 
has not yet been obtained, or with the hope that 
the serum will influence favorably secondary in- 
fections with the streptococcus. The serums of 
■^.ronson, Moser and of Menzer have been tried 
inore than others. Moser is probably more enthu- 
siastic than others, and he claims a reduction in 
the mortality from an average of 13.08 per cent, 
to 8.9 per cent, in 400 cases. Others have observed 
a favorable influence in some cases, but the re- 
sults are not uniform. The development of sec- 
ondary streptococcus infections can not be pre- 
vented by the use of the serums, although it is 
stated that their severity may be moderated. 

Of theoretical interest is the report by Weiss- 
becker and by v. Leyden that the serum of con- 
valescents causes a reduction of the temperature 
and a shortening of the course of the disease. 

The results published up to the present time 
indicate that we have not as yet an efficient serum 
for scarlet fever (see also p. 527). 



Serum 

Therapy. 



X. MEASLES. 

Bacilli which have been recognized in the con- 
junctiva, sputum and nasal passages in cases of or8;a 
measles have, for the most part, resembled either 
the diphtheria or the influenza bacillus. Pseudo- 
diphtheria bacilli are normal residents in the eye, 



liisiits. 



INFECTION AND IMMUNITY. 

and influenza-like bacilli are found in the sputum 
in various conditions; hence, there is insufficient 
reason to associate such organisms with the etiol- 
<»L r v of measles. The micrococci found by Lasage 
i L900) have noi received recognition as the cause 
of the dis< 

Measles ia highly contagious, even during the 
prodromal stage. The contagion doubtless is 

I from the lungs as Well as the skin. and. in 
view of the early bronchial symptoms, the virus 
probably gains entrance through the lungs. Suc- 
cessful inoculation into man with hlood taken 
from the involved skin shows that the virus exists 
in the circulation of the skin. Hektoen doubts 
the decisiveness of a number of these experiments 
since they were carried out in the presence of 
epidemics and natural infection could not be ex- 
eluded ; at the sane time he does not question the 
results of Mayr ( L852). In two experiments on mar; 
Eektoen determined the presence of the virus in the 
blood. "The results of these two experiments per- 
mit the conclusion that the virus of measles is 
present in the blood of patients with typical 
measles some time at least during the first 30 
hours of the eruption ; furthermore, that the virus 
retains its virulence for at least 24 hours when 
such blood is inoculated into ascites-broth and kept 
at 37° C. This demonstration shows that it is 
not difficult to obtain the virus of measles unmixed 
with other microbes and in such form that it may 
be studied by various methods." The virus is 
much less resistant than that of scarlet fever. The 
varying grades of severity of different epidemics 
show that it is subject to alteration in its virulence. 



MEASLES. 



749 



Although measles is considered somewhat harm- Effect on 
less on the whole, dangerous complications, such 
as broncho-pneumonia and otitis media, are suffi- 
ciently frequent. The development of tuberculosis 
following measles, an event which is not uncom- 
mon, shows that measles may greatly decrease gen- 
eral resistance. 

The proplrylaxis of measles is not different from Prophylaxis. 
that of other exanthemata. The isolation should 
continue for four weeks after the appearance of the 
exanthem (Grotschlich). The sickroom should be 
disinfected eventually. The view not uncommonly 
encountered that measles is a good thing for a 
child to have and be over with is in no way justifi- 
able. The development of serious complications 
can in no case be foreseen, and fatalities may occur 
even in mild epidemics. 

Very young children, the rachitic and tubercu- suscepti- 

J J ° 3 bility and 

lous, and those in a poor state of nutrition should Recurrence, 
be guarded against exposure, for in them measles 
is often malignant. Infants are less susceptible 
than older children. Measles occurs in adults more 
frequently than scarlet fever. Eecurrences, on the 
whole, are frequent, as many as four attacks hav- 
ing been noted in an individual. Hence, the im- 
munity caused by infection is not uniformly of a 
permanent character. 

It is very probable that the inhabitants of a 
country in which measles is endemic gradually 
become immunized, with the result that the disease 
prevails in a mild form. On the contrary, regions 
in which measles has hitherto been unknown, or 
has been absent for many decades, are susceptible 
to -visitations of great malignancy. Such epi- 



Racial 

Immuniza- 
tion. 



750 /\ FECTIO* I \/> JM l// Ml) 

demies have occurred in the Faroe Islands and in 

Iceland, with a mortality exceeded by few epi- 
demic di» 

A moderate Ieucocytosia is excited in measles, 
"which begins bood after infection, reaches its 
maximum six days before the appearance of the 

eruption, ami lasts into the first part of the stage 

of invasion" (Tiliston). We are ignorant of the 
significance of this leucocM tosis. 
T re is no Berum therapy for measles. Weiss- 
■ i- states that the serum of convalescents in- 
flueni dis ase favorably. 

XI. oia.Wl w MEASLES ( ROTHELN ). 

Rotheln is considered as distincl from-measles, 
in Bpite of clinical similarities. It is recognized 
because of certain peculiarities in the eruption and 
its uniformly mild course. Perhaps the strongest 

-■ 9 to he <list i net 

lies in the fact that an attack' of rotheln does not 

an immunity against meae 

Rotheln is contagious. Efforts should he made 

to prevent extension, as in measles, the methods of 

transmission being the same in the two diseases. 

xir. whooping COUGH. 

Various protozoa (?) and bacteria (cocci and 
bacilli) have been assigned as the cause of whoop- 
ing cough. Many of the so-called protozoa found 
in the throat were undoubtedly tissue cells (leuco- 
cytes, ciliated epithelium). Among the cocci, the 
diplococcus of Ritter (1892) acquired some promi- 
nence. He is said to have found it constantly in 
146 cases. Investigations by others failed to jus- 
tify his conclusions. 



/ 



I'ERTUtiSIS. 



751 



Disregarding some other bacilli which certain The influ- 
investigators have attempted to bring into rela- Bacillus of 
tion with pertussis, we may note the essential facts a nd e, o? leP 
concerning an influenza-like bacillus which has JOC, "" a,,ni 
been found with great constancy and by many 
competent investigators in the sputum of patients. 
First observed by Sprengler (1897) in pertussis 
sputum, this organism or bacilli similar to it have 
been found by Czaplewski and Hensel, Zusch, 
Cavasse, Vincenzi, Elmassian, Luzzatto, Arnheim, 
Jochmann and Kruse, Beyher, Smit. Wollstein, 
and Davis. The organism is said to be somewhat 
larger and thicker than the true influenza bacillus, 
but has the same bipolar staining affinity and the 
same demand for hemoglobin for its growth in 
pure cultures. There is some difference of opinion 
as to whether the organisms described by these 
different observers are all identical and as to 
whether all have worked with pure cultures. The 
conclusion of Davis would seem to sum up the 
situation: "With the exception of Manicatide, 
probably all of the investigators, at least in more 
recent years, have been dealing, either in pure or 
impure cultures, with the influenza-like bacillus, 
first described by Sprengler and later by Joch- 
mann." Culturally they are not to be differen- 
tiated from the influenza bacillus. When in pure 
culture they demand hemoglobin for their develop- 
ment, although the amount of hemoglobin may be 
so small as not to color the medium. When in 
mixed culture with the streptococcus, staphylo- 
coccus, pneumococcus and B. xerosis, they grow 
abundantly even in the absence of hemoglobin. 
Hence, in relation to symbiosis, also they resemble 
the influenza bacillus. For symbiotic development 



Hemophilic 
Properties 
and Sym- 
biosis. 



INFECTION AND IMMUNITY, 

it i< necessary that the secondary organisms be 

living; when killed or when the filtrates of bouil- 
lon cultures are used, the "pertussis bacilli" are 
not stimulated to growth. 
Patao*ea- In<vulation of pure cultures on the mucous 
membrane of the upper respiratory passages in 
various animals, including the monkey, does not 
produce a pertussis-like infection. The organisms 
have, however, a low degree of virulence for ani- 
mals, particularly the guinea-pig. Davis found 
that three blood-agar cultures injected intraperi- 
ally killed guinea-pigs in 24 hours or less. 
lg augmented whei 
mixed with certain other bacteria. By injecting it. 
mixed with a Don-pathogenic staphylococcus, its 
virulence, after six passages, was so increased that 
blood-agar culture killed guinea-pigs in 24 
hours (Davis). In this respect, also, it resembles 
bacillus. 
iffniacance. [noculated in the throat of an adult, who pre- 
sumedly had never had whooping cough, a distinct 
rile reaction, lasting two or three days, devel- 
oped after an incubation period of two days 
(Davis). Headache and pharyngitis were accom- 
paniments of the reaction and the pharyngitis 
continued for at least four weeks. There was lit- 
tle cough, and it was concluded that the micro- 
organism had not produced wdiooping cough, 
although it had shown toxic and infec- 
tious properties. The bacillus proliferated enor- 
mously in the pharynx and nose and was still to 
be cultivated after four weeks. Such an organism 
may well be an important factor in whooping 
cough, even though it is not the essential cause. 
Davis is inclined to regard its relation to whoop- 



PERTUSSIS. 753 

ing cough as similar to that of the streptococcus 
to scarlet fever — i. e., a very important compli- 
cating organism. 

Davis finds still further reason for doubting its 
specific relationship to whooping cough from the 
fact that it was found frequently in measles, acute 
influenza, epidemic meningitis, bronchitis, vari- 
cella and in normal throats. 

In 1906 Bordet and Gengou isolated a bacillus Bacillus of 
from cases of whooping cough and gave the fol- Gengou? 11 * 
lowing reasons for believing that it was the spe- 
cific etiologic factor in this disease : 1. The organ- 
ism is found in overwhelming numbers during the 
early course of the disease and in almost pure cul- 
ture. 2. The bacilli as antigen give a comple- 
ment-fixation reaction with the serum of pertussis 
patients and this reaction does not occur with 
other bacteria associated with the disease. 

The organism is a short, polar-staining ovoid 
resembling the influenza bacillus but slightly lar- 
ger. Bordet and Gengou grew the organisms on a 
culture medium made up of a glycerin-potatoe- 
blood-agar mixture. On this medium the organ- 
ism grows kkthe form of a delicate film made up 
of very small colonies and changes the medium to 
a dark brownish color. 

Wollstein was able to confirm the finding of 
the bacillus in the early stages of pertussis, but 
failed to obtain the complement-deviation reac- 
tion. Agglutination was very irregular and no 
immune opsonins were found. The etiologic rela- 
tionship of the organism to whooping cough is at 
present uncertain. 

The organism is disseminated extensively by 
coughing, and the same is probably true of the es- 



754 /Ml.' il<>\ a.\J) IMMUNITY. 

contiiKiouK- Bential virus. Close contact, aa by kissing, or the 
common use of eating utensils is a means of trans- 
mission. The opinion has been advanced by Weill 
an<l Pehn that pertussis is contagious only during 
the catarrhal stage of the disease. "Of ninety- 
three non-immune children who were placed with 
fifteen children who were in the convulsive - 
oone became sick" (cited by Gotschlich). This 
point is not sufficiently established, however, to 
warrant modifications of prophylactic measures. 
Whooping cough is often epidemic ami is more 
common In cities where contaci with the infected 
is more Likely to occur than in the country The 
incubation period is from seven to fourteen days. 

Isolation is more difficult than in the more acute 
contagious diseases, yet contaci with other chil- 
dren should he avoided SS in in T i as possible, and 
the patients should he withdrawn from school 

until iv, omplete. 

Pi : .most exclusively a chil- 

dren, although older people may he attacked. Sus- 
ceptibility is not general One attack usually con- 
immunity. A varying degree of leucocytosis 
lied by the infection (12,000 to 45,000), the 
Lficance of which is not known. It is chiefly 
mononuclear. 
Serotherapy. Serotherapy for whooping cough has not ad- 
vanced to a point where we can speak with as- 
surance concerning it. Manicatide (1903) im- 
munized horses and sheep with the organism which 
he cultivated from a large number of cases. He 
reports that cure may be accomplished in from 
two to twelve days when the serum is used within 
the first fifteen days of the disease. The bacillus of 
Manicatide differs from the influenza-like organ- 



MUMPS. 755 

ism of other observers, hence, his antiserum cau 
not be accepted unreservedly as a specific serum 
for whooping cough. Smit found that an anti- 
serum for the influenza-like organism exerted no 
influence on the disease. Bordet found the serum 
of a horse immunized to his bacillus of question- 
able curative value. 

XIII. MUMPS (EPIDEMIC PAROTITIS). 

Mumps occurs epidemically in children, particu- 
larly in schools, in other institutions, and in sol- 
diers confined to barracks. It is most frequent in 
the spring and autumn and probably is endemic in 
large centers of population. It is contagious, the 
virus probably being disseminated from the upper 
respiratory passages with infected droplets of spu- 
tum and saliva. The disease has an incubation 
period of two to three weeks and runs its course 
in from seven to ten days. 

Involvement of the testis, ovary or female breast 
are complications to be feared in adult life ; "orchi- 
tis, albuminuria, with convulsions, acute uremia, 
endocarditis and peripheral neuritis are occasional 
complications" (Osier). Fatal meningitis devel- 
ops rarely. Very young infants and adults are at- 
tacked less frequently than children of school age. 

In 1893, Laveran and Catrin described a diplo- pipiococci 
coccus obtained by aspiration of the exudate in the ln Munrpsi - 
parotid gland. The organism was also isolated 
from the testicle in orchitis cases and from the 
circulating blood. Since that time, diplococci 
have been isolated from cases of mumps by a num- 
ber of observers. In 1909, Herb isolated a cliplo- 
coccus which she considers as probably identical 
with the organisms described by previous writers. 



756 IXILCI 1<>\ _\\n l 1/ 1// A/7 \ . 

The organism was cultivated at autopsy from 
the lung, testicle, cerebrospinal fluid, bile, parotid 
gland and pericardia] fluid. The coccus 
Gram-positive organism occurring mostly in pairs 
but also in short chains and small groups. It 
varies from 0.5 to 0.8 microns In diameter in 
twenty-four-hour cultures. It is non-motile, lias 
no capsule, and forms do gas or indol. It grows 
Blowly on ordinary media and much more rapidly 
on media containing saliva. The growth on saliva 
agar appears as pearly white pin-point <H 

Colo; 

Pathoven- t _ 3m is fata] to white mice, white rats, 

guinea-pigs and rabbits when injected suhcutan- 

:im injected into Steno's duct in mon- 

- QOn-SUppurative parotitis was pro- 
duced and occasionally an orchitis. The evidence 
indicates strongly that the diplococcus described 

tor in mumps. 

immunity. ,,,,. a ftack g s establishes protection. Ac- 

ing to I [i rb, I - would Beem to play 

an important part in the protection of the body 

jainst mumps. 

Patients should d for three wi 

from the time symptoms appear. 

XIV. EPIDEMIC POLIOMYELITIS. 

Epidemic poliomyelitis, or acute anterior mye- 
litis, is an acute febrile disease of children and 
young adults accompanied by an acute inflamma- 
tion of the cord and brain. Clinically, it is char- 
acterized by paralysis of various muscles, usually 
those of the extremities. The paralysis is very 
rapid in onset and varies in tendency to recovery 
and permanent disability. 



POLIOMYELITIS. 757 

The disease has been known for over half a cen- 
tury, but it has been recognized as an infectious 
disease for only a few years. 

Although various bacteria have been described Micro- 
in connection with the disease, there has been little 
reason for considering them other than mixed in- 
fections or contaminations. 

Flexner and Lewis found that the virus of 
poliomyelitis is filterable and describe very minute 
bodies occurring in the infectious- nitrate. The 
bodies can be stained with Loeffler's flagella stain 
and cause a cloudiness in culture media after suit- 
able incubation. The transfer of a small amount 
of such cloudy media to a second clear media re- 
sults again in cloudiness after incubation. The 
virus loses its virulence when heated to from 45° 
to 50° C. for half an hour, but resists freezing. 

Landsteiner and Popper, in 1909, and Knopf el- Experimental 
macher a little later, succeeded in producing polio- Poliom ^ elitis - 
myelitis in monkeys by injection of emulsified 
cords of children dying of the disease. They were 
unable to infect second animals with material 
from the first. Later, in 1909, Flexner and Lewis 
were able to produce poliomyelitis in monkeys in 
a way similar to that described by Landsteiner 
and Popper, and succeeded in transmitting the 
disease from one monkey to another. 

Infection may be produced in monkeys by in- 
jecting the virus into the brain, spinal canal sub- 
cutaneous tissue, peritoneal cavity or into the large 
nerves. 

Experimental poliomyelitis can be produced by Jf "uJj'viiS* 
the injection of material from the blood at the 
beginning of the infection and by injection of 



/ \ I Id ln\ I \ l> /MMI Ml). 

emulsions from the nasopharyngeal mucous mem- 
brane. The emulsions of central nervous tissues 
the mosl constanl results, while the emul- 
sions of other organs such as liver, spleen and 
bone marrow have Failed to give results. It is 
3ible thai infection takes place in a manner 
similar to the process in epidemic meningitis. 
Thai is by dissemination of droplets and particles 
from the nasopharyngeal membrane. 

In a reinooulation of ten monkeys which had 
ivered from poliomyelitis, Flexner and Lewis 
observed DO instant mi! attack-. In nor- 

mal monkeys 72 per cent, of those inoculated he- 
came infect. -.I and showed paralysis. Those which 
did not become paralyzed were Buspected of mild 
attacks. It is possible that vaccination may he 
successful. 

XV. NOMA. 

Noma, or gai stomatitis, is a somewhal 

rare disease of children whose resistance is low- 
ered by the acute infectious diseases. Among these 
it is found most frequently associated with meas- 
\e\t to measles, it i- oftenest found in 
typhoid, intermittent fever mercurialism, scarlel 
fever, pertussis, enteritis, variola ami many other 
diseae -. 
Pnaiforiu Perthes, Seiffert, Mafzenaur and others found 

Baellll and 

spirilla, associated with noma, fusiform bacilli and spirilla. 
These observations have since been confirmed by 
many others. The organisms are found in the 
necrotic tissues and especially at the line of ad- 
vancing necrosis. Ellerman, in 1904, cultivated 
fusiform bacilli from a case of noma. Weaver 
and Tunnicliff obtained pure cultures of fusiform 



NOMA. 759 

bacilli from noma in 1905. The organism is an 
obligative anaerobe requiring a temperature of 
about 37° C. for growth. The presence of blood 
serum or ascites fluid is necessary for obtaining 
the best growth, but cultures can be obtained on 
glycerin agar. All cultures have a foul odor. 

On ascites agar the bacilli occur as delicate 
pointed Gram-negative rods. In ascites broth the 
organisms are more slender, not so pointed, and 
tend to form chains. On solid media wavy fila- 
ments are found. In old cultures forms similar 
to the spirilla found in the tissues were found. 
Tunnicliff isolated from the gums of healthy sub- 
jects, fusiform bacilli which were apparently iden- 
tical in cultural characteristics and morphology 
with those found in noma. In pure cultures 
grown several days spirilla were found rather con- 
stantly and it would seem as if the spirilla were 
simply a stage in the development of the fusiform 
bacilli. 

The number of cases in which the bacilli and 
spirilla have been found associated with noma 
makes it strongly probable that they are the cause 
of the disease. 

Fusiform bacilli and spirilla similar to those 
isolated from noma have been found in ulcero- 
membranous angina and stomatitis, in hospital 
gangrene and in fetid infections in various parts 
of the bodv. 



INDEX 



PAGE 

Abrin 21, 218 

Achalme, bacillus of, in rheumatic fever 525 

Acne, staphylococcus in 543 

Acquired Immunity (see Immunity, acquired). 
Active immunity (see Immunity, active). 

Actinomyces bovis et hominis (ray fungus) 25. 629 

Classification of, 630, 631 ; cultivation and morphol- 
ogy of, 630 ; lungs in, 502 ; occurrence of, in Na- 
ture, 631 ; resistance of, 630 ; species of, and viru- 
lence of, 631. 

Actinomycosis 25, 629, 633 

Animals, susceptibility of, to, 629 ; fibrous tissue 
formation in, 629, 632 ; immunity and susceptibil- 
ity to, 632 ; infection atria, 631 ; iodid of potassium 
in, 633 ; lesions, character of, 632 ; phagocytosis in, 
632 ; prophylaxis of, 632 ; transmission of, 631. 
Acute articular rheumatism (see Rheumatic fever) . . . 729 

Adrenal gland, cytotoxin for 304 

Agglutination 206, 219 

Of erythrocytes, 218 ; of erythrocytes with silicic acid, 
244 ; etiology, determined by, 23 ; group agglutina- 
tion, 224, 227 ; immunity, relation to, 207, 208 ; 
macroscopic and microscopic, 216, 217 ; prognostic 
importance of, 209 ; sodium chlorid, influence on, 
224 : stages in the reaction, 224 ; substances con- 
cerned, 216 ; serum dilutions, 227 ; specificity, 225 ; 
technic, 212 ; theories of mechanism of, 230 ; see 
also under Agglutinins and under different diseases 
and micro-organisms. 

Agglutinins 206-218 

Absorption of by bacteria, 347 ; agglutinophorous 
group, 222 ; auto-agglutinins, 218 ; chief agglutinins, 
225 ; congenital, 207, 210 ; definition, 219 ; distri- 
bution of, in the body, 210 ; Ehrlich's theory of the 
production of, 228 ; ferments, action of, on, 210, 
221 ; formation of, following vaccination, 377 ; 
haptophorous group of, 222 ; H auptagglutinin , 225 ; 
immune, 174, 207 ; isoagglutinins, 218 ; mixed infec- 
tions, influence of, on, 227 ; Mit agglutinin, 223 ; 
normal, 223 ; origin of, 210 ; precipitation of, by 
chemicals, 221 ; production of, 207 ; receptors of 
second order, 222 ; resistance to acids and alkalies, 
223 ; resistance to heat, 211, 222, 223 ; somatic and 
flagellar, 221 ; specificity of, 206 ; structure of, 222 ; 
union with cells, character of, 347, 348 ; unit of 
measure of, 217 ; variations of. in animals, 228 ; 
variations in the quantity of, 209 ; zvmotoxic group 
of, 222 ; see Agglutination, Agglutinogens, Agglu- 
tinoids, and also under the different micro-organ- 
isms. 
Agglutinogen^ power of bacteria 208 



762 INDEX. 

Agglutinogens, or agglatinable substances 218 

DlnTusIbtlity of, 221; distribution of, 220; flagellar 
and somatic, 221 ; multiplicity of, 221 ; resistance 
of, i" heat, 221 ; structure ol 2 Agglutinins 

and Agglutination. 

Agglutlnolds 223 

Aggressins L22, 33G 

Allergy (see Anaphylaxis). 

Alexins 160, 24S 

Definition of, 150; Identity of, with complement. 249, 
250; nature and selective action of, 246; se< Com 
plement 
Alkaloids. 

Failure to cause formation of antibodies, 342; state 
of, within the cells, 342, 349 

Amboceptold 353 

Amboceptors 249, 256 

Absorption of, by cells, 259, 261, 347; bacteriolytic, 
258; complementophlloua baptopbore <>i". l it : cyto- 
phllous haptophore «•!". 262; formation ><(. 264; 
formation following vaccination, 378; hemolytic 
Influence In phagocytosis, 320 ; Isolation <>i'. 
260; manner of action of with complement, 260; 

•_•<;"_'. 351, 352; occurrei f, In animal Becretlons, 

27 » : origin from leucocytes. 313, 320; origin In 

cholera, 820 ; r< I he third order, 35 1 ; 

* Izatlon i>\ 258 ; 

■ are of, 262 : Bynonyms 

mion with cells, nature of, 262, 

• i [emolj -in- I serum i . Bacterlo- 

lyali i Venoms. 

Ann bo - oh 

Discovery ol hogenlcity of. 688; Bymblosis 

of, 687, 688 : - Ami bic dysentery. 

i mi ba proti us 

Ameba. 
Cultivation and distribution of. ,- > s 7 : phagocytic 
action of, 306; resistance of, 687; symbiosis, 687, 
688. 

Amebic dysentery 686 

Anatomic changes In, 689; Immunitj to, 690; liver 
abscess In, 689 : Occurrence of, 689 ; prophylaxis, 
689 : see a meba?, and Amt '»i coli 

Amibodiastase 306 

Amyloid degeneration, production of, by Btaphyl >ccus. 542 

Anaphylaxis. 
Acquired, 384; active, 384; anaphylactic shock, 392; 
anaphylotoxln, 390; antianapnylactlc state, 393; 
antibody In, 388; antigen In, 385; complement in, 
390; natural, 384; passive, 384; relation to revac- 
cinatlon, 381; relation t<> primary toxicity, 386: 
relation to tuberculin, 395; relation to serum dis- 
ease, 396; sensitization in, 386; theories '>f, 391. 
"Anatomic tubercle" (see Tuberculosis). 
Animals, susceptibility of, to. 

Actinomycosis, t;::i : anthrax. 4'.»4. -4f»r, ; B. influenza, 
565; 7>. melitensis } 500; cholera, 474; hydrophobia. 
i<>4. 705; leprosy, 618; Micrococcus ratarrhalis, 
551 ; Micrococcus meningitidis, 558 : oidiomycosis, 
639. 640: pnoumococcus. 504; pseudotuberculosis, 
014: relapsing fever. 04.".: staphylococcus. 375. 376: 
streptococcus." 543 : syphilis, 648. (',40; trypanosomi- 



INDEX. 763 

r.\<;i-: 
asis, 679, 680, 681, 682 ; tuberculin, 581 ; tuberculo- 
sis, 593, 594, 611, 612. 

Animal experiments, in testing' value of serums 345 

Anopheles mosquitoes. 

A. macuiipenn-is, 664, 665; A. iinctipennis, 664: habits 
of, 664, 665 ; life cycle of. 665, 666 ; malaria, role 
in, 654 ; migration of, 666 ; occurrence, 664. 

Aiithracase-Immunprotciden 407 

Anthrax 492, 49S 

Animals, immunity and susceptibility of, 495, 496 ; 
bacillemia, 493 ; discovery of its microbic nature, 
4, 5, 6 : immunity, 496 ; immunization, mixed, 498 ; 
influence of streptococcus on, 528 ; malignant pus- 
tule, 494 ; occurrence, 492 ; opsonins, 497, 498 : 
phagocytosis in, 316, 496 ; prophylaxis, 495 ; sero- 
therapy, 497 ; toxic results, 495 ; transmission, 494 ; 
vaccination, 5, 6, 497 ; wool-sorters' disease, 495 ; 
see also B. anthraeis. 

Antiabrin 203 

Antiaggressins 338 

Antiamboceptors 270 

Danger in formation of, 272 ; as receptors of the first 
order, 351. 

Antibacterial serums (see Bacteriolysins) 370-375 

Antibodies. 

Mechanism of production, 343 ; origin of, 354, 480 ; 
scheme of, 360 ; specificity of. 352 ; union with anti- 
gens, 344 ; see Antitoxins, Amboceptors, Agglutin- 
ins, Precipitins, Hemolysins, Bacteriolysins and 
Cytotoxins. 

Anticomplements 269, 2S0, 351 

Anticrotin 203 

Anticytotoxins 295, 361 

Antiferments 175, 204 

Antigen of Wassermann test 287 

Antigens. 

Scheme of, 360 ; union with tissue cells, character 
of. 344. 

Antiglobulin 239 

Anti-immune serum 270 

Antilaccase 204 

Antileucocidin 203, 539 

Antileucotoxic serum 291) 

Antinephrotoxin 300 

Antinenrotoxin 301 

For venom, 430. 

Antipepsin 204 

Antiprecipitins 23S 

Antirennet 204 

Antiricin 203, 345, 346 

Antirobin 203 

Antispermotoxin 296 

Antistaphylolysin 547 

Antisteapsin 204 

Antistreptocolvsin 519 

Antitoxins 167, 204, 365, 39S 

Earlv administration of, 367, 368 : curative action of, 
366, 367 ; discovery of. 10 ; examination of by U. S. 
Hygienic Laboratorv, 188 ; for animal toxins, 203 : 
for B. botulinis, 525 : for B. diphtheria, 404. 406 ; 
for B. pyocyaneus, 424 : for B. tetani, 367, 416 ; 
for bacterial toxins, 203: for plant toxins (abrin, 
crotin, ricin, robin, phallin), 203, 427: for pollen 



764 INDEX. 

i -a- . i: 

toxin, 420; for soOtoxins, 431; formation of, 198: 
baptophorous group of, 192; Infections characterised 
by formation of, 398, 431; leucocytlc origin, ques- 
ti"n of. 321; manufacture of, 180: mode of action 

of, .".i". 365. 370; nature <>i". 321; toxins, neu- 
tralization of, by, 191. 345, 846; normal. 147; 
preservation of, 182, 184; prophylactic action of, 
370; receptors, free, 202; receptors o£ the flrsl 
order, •"••"•i : relation of, to toxins, in the body. 
relation of, to toxins, In vitro, ::•'..".: standardization 
of, 183, 419; anil of. 183; see Pari II. Group I. and 
also Hi-- different micro organisms. 

Antitrypsin 204 

An tl urease •_•" t 

Antlvenin 181, 203, 133 

Antltj : 204 

Arachu< lye in i spider poison i 204 

Arrhenius and Madsen, views of 354 

Arthritis 509, 514, 520. 545, 553, ."..v 

Arthus' phenomenon 

Aspergillus 21, 641 

Atrophy, phagocytosis In 308, 309 

.\ ttenuatlon. 

Importance of in vaccination, 166; methods of, 363. 

igglutlnlns -i s 

Autocytotoxins 293, 305 

Autolytic products, vaccination with 364, i . T 

Autonephrotoxins 299 

Autopreclpltins 236 

Autospermotoxin 296 

Bacillus afrogem s causulatus 29, 526 

Bacillus alcaligi net 434 

Bacillus anthracis 25, 192,494 

Antagonism of, by other bacteria, 104; antiserums 
for, '•' : attenuation of, 166, 363; cultivation of, 194; 
discovery of, 4, 493; gastric Juice, effect of, on, 
in. 494; Immunity, active, 497; Immunity, ac- 
quired, 316, 196: Immunity, natural, 496; Immu- 
nity, passive, I'.'T : Infection atria, 141 : opsonins, 
197; phagocytosis of. 196; serums, 'fT« •« t of, on, 
496; Bpores of, 6, 493; toxic properties of, 495; 
virulence Anthrax. 

Bacillus botulinus 410, 420 

Animal-, susceptibility of. 421, 422; antitoxin tor. 

422 : morphology, etc, 4U" ; occurrence in meat, 
420; saprophytic nature of, -4 ii l : spores of, 420; 

t<»xin. action of, -ii'i ; toxin, detection of in meat, 
420; toxin, preparation and resistance of, 421; 
Botulism. 
Bacillus chancri mollis (bacillus of Ducrey ; bacillus of 

soft chancre i 569 

Cultivation, morphology, phagocytosis of. suscepti- 
bility of animals to. 570. 

Bacillus of chicken cholera 106 

Bacillus coli communis 463, 409 

Agglutination of. 206, 208, 225, 400: antagonism 
for putrefactive bacteria. 4d4. 4<;r, ; antiserums, 
properties of, 40S ; beneficial functions of, 464 : in 
cystitis. 468; in enteritis. 142. 400. 408; group 
agglutination. 225 ; group of. 403 : in meningitis, 
."•; : morphology and staining of. 403 : occurrences 
in intestines. 403. 464: occurrence in Nature, 463; 
in pneumonia. .".02 : resistance of. 403. 404 ; serums, 






INDEX. 705 

PAGE 

effect of, on, 464 ; cymbiosis with Anieba coli, 087 ; 
toxin of, 468 ; typical strains of, 464 ; virulence of, 
465, 466, 467. 

Bacillus diphtheriw 25, 398, 399 

Agglutination of, 407 ; antitoxin for, 203, 404, 406 ; 
morphology, staining, cultivation, resistance, via- 
bility of, 399 ; occurrence of, in the body, 400, 401 ; 
pneumonia, in, 502 ; toxic action of, 31, 32 ; toxins 
of, 177, 178, 400. 401, 406 ; toxin, attenuation of, 
142, 363 ; tuberculosis, in, 591 ; see Diphtheria. 
Bacillus of Ducrey. See Bacillus cliancri mollis. 

Bacillus dysenteric 25, 453, 455 

Agglutination of, 206, 208, 453, 454 ; antiserums for, 
properties of, 458 ; cultivation and morphology of. 
453, 454 ; dissemination of, 457 ; endotoxin of, 456 ; 
etiologic role of, 454 ; "Flexner" type of, 453 ; 
pseudodysentery bacilli, 453 ; toxicity of, 456 ; toxin, 
autolytic, of, 456 ; types of, 453 ; see Dysentery, 
acute epidemic. 

Bacillus edema? maligna? 13, 29 

Bacillus enteritidis 459-463 

Agglutinins and agglutination of, 208, 463 ; Bacillus 
paratyphosus, resemblance to, 450 ; discovery of, 
460 ; fermenting powers of, 460 ; group agglutina- 
tion, 225 ; group of, 460 ; meat poisoning by, 459 
463 ; morphology and staining of, 460 ; occurrence 
of, in meat of horses and cattle, 460, 461, 462 ; 
poisoning by oysters and fish, in, 462 ; resistance 
of, 462 ; toxin, 460, 461 ; toxin, occurrence in meat, 
462 ; toxin, resistance of, 462. 
Bacillus of Friedlander ; see Bacillus pneumonic 

Bacilli from butter, grass and milk 614 

Bacillus icteroides. in yellow fever 712, 713 

Bacillus influenza? 25, 564 

Agglutination of, 569 ; animals, virulence for, 565 ; 
antiserum, properties of, 569 ; in conjunctivitis, 566 ; 
cultivation of, 564 ; discovery of, 564 ; excretion of, 
565 ; hemophilic properties of, 564 ; immunization 
with, 569 ; in meningitis, 556-566 ; morphology and 
staining of, 564 ; occurrence of, in the body, 566 ; 
otitis media, in, 566 ; peritonitis, in, 566 ; resist- 
ance of, 565 ; symbiosis of, 564 ; toxin of, 565 ; 
tuberculosis, in, 591 ; see Influenza. 
Bacillus lactis aerogenes. 

Antagonistic action on putrefactive bacteria, 465 ; 
occurrence in intestines, 571. 

Bacillus lepra? 25, 616 

Antiserums for, 623 ; discovery of, 616 ; endotoxin, 
question of, 621 ; excretion and occurrence in 
nature of, 619 ; morphology of, 616 ; occurrence 
in the body, 620 ; phagocytosis of, 620, 622 ; see 
Leprosy. 

Bacillus of Lustgarten 613 

Bacillus mallei 25, 625 

Agglutination of, 627, cultivation, morphology and 
resistance of, 624 ; mallein. varieties and prepara- 
tion of, 625 ; meningitis, in, 556 ; phagocytosis of, 
627. 

Bacillus melitensis 500 

Agglutination of, 499 ; animals, susceptibility of, to, 
500 ; morphology of, 499 ; opsonins, influence of 
in phagocytosis of, 499 ; serums, effect of, on, 499 ; 
see Malta fever. 



766 INDE \. 

Bacillus in , i ilatu* .".71 

Bacillus of ozena .'.Tu 

Bacillus paratyphosus 149 

tlnation of, h'.'. ir.L' : antiserums for, properties 

152; bl i cultures, 153; endotoxin, 452; ezcre 

tion of, i.". i : meal poisoning by, 450 : occurrence In 
Hi body, 15 l : "paracolon" bacilli, relation to, 
t:." : resistance of. i"-i . toxicity, 452; types of, 
oral \ ph. .id fever. 

Bacillus peetis 25, 4M 184 

Agglutination of. 208, 191; cultivation of. 181, 182; 
endotoxin, resistance of, i84 ; Involution forms, 182; 
meningitis, in. 556; morphology, 481; phagocytosis 

190; pleomorphlsm, 481 : pneumonia, in. 
resistance and viability, 182, 183 : staining of, «m : 
toxicity of cell bodies, im : toxin of Lustlg and 
Galeottl, im : toxin, Boluble, question of, 183; vim- 
184, i v ". : see Plague. 
Bacillus pneumonia (bacillus of FYiedlander) . .502, 571, 572 
Agglutination of, 208, 572: antagonism for /;. anthra- 
' : - 56 . ; lesions 

572 meningitis, In, :.."><'.: pneumonia, In, 
10, 572 : tuben ufosls, ii 
Bacillut 

Antagonism for /;. anthracis, 494; Coley's mixture, In, 
:.•_•:• ; Bi rabiotic a< I 

Baclll 208, 225 

Bacillus /<■•" udotubt n ulosis, varieties of 615 

Bacillus pyocvam us 122-425 

Agglutination of, 206. 208; agglutinins for, 125; 
tal Invasion by, 422; antagonism for /.'. anthra- 
\in. 12 1 : bactericidal -.ruin for, 
194 ; fei a ; endocarditis, In, 422 : endo- 

i 13 : Infections, symp- 
toms of, 424; meningitis, In, 123; pigments of, 424; 
pyocyanae . 124; pyocyanolysin, 124; pyocyanln, 
4 J i ; secondary in !".■»;_ sepl Icemia In, 

toxin, soluble, 17 7. 124, r_'.". : tuberculosis In, 

r rhlnoscleroma "'7l' 

Bacillus of symptomatic anthrai 315 

Bacillus t( tani 108-419 

Agglutination, 119; anaerobic property of, 110; ani- 
ptibillty of, i" toxin, 156; avlrulenl 
strain-. } 1 1' : discovery of 408; morphology, stain- 
cultivation, 408, 409; occurrence In Intestines, 
409; occurrence in nature, -4"'.' : parasitic power of, 
-4111 : pathogenic properties of, 413; resistance of 
- of, 4in; toxins ..i". 177. 1 78, 4 1 2 : toxin, ab- 
sorption "i". by leucocytes, 321; toxin, fixation of, 
by tissues, 156, 157, 348, 349, 366, 411; toxin, 
attenuation of, 363; toxin, action of gastric juice 
<>n. 141': toxin, neutralization of, by antitoxin. :;<;s •. 
action of pancreatic juice on, 14:;: virulence, 315; 
tanus. 

Bacillus tal!' rculosis 25. 573 

Agglutination, 608, 610; agglutination, relation of to 
immunity. 211 : animals, susceptibility of to. 593 ; 
antiserums, properties of, 608; attenuation of, 576; 
avian. 612 : bacteria resembling. 613 ; bovine, differ- 
entiation of from human. 583 : constituents, 577 ; 
cultivation, r.75 : discovery of, 573 : effect on tissues. 
144. 146, 588-591; excretion of. 581. 582, 586; 



INDEX. 707 

PAGE 

fever producing substance of, 577 ; of fish, 013 ; 
gastric juice, resistance to, 141, 576 ; immunization 
with, 577, 598, 599 ; inflammation of lungs, in. 
502 ; lesions produced by, 577 ; morphology of. 574 ; 
occurrence in nature. 581 ; pathogenic properties of, 
r>77 ; phagocytosis of, 588, 589 ; proteins in, 577 ; 
resistance of, 576 ; staining properties of. 575. 577 ; 
streptococcus, influence of. on cultures, 522 ; "tox- 
albumin" of, 578 ; toxic substances, effects of. 577 ; 
toxins, 60S, 610 ; virulence of, 577, 594 ; see Tuber- 
culosis. 

Bacillus typhosus 25, 433 

Agglutination of, 2U6, 207, 230, 448, 449 ; antitoxin, 
question of. 435 ; autolysis of. 435 ; blood cultures 
of, 437, 449 ; discovery of, 433 ; dissemination of, 
434 ; endotoxin, 435 ; excretion of. 438 ; extracts of, 
447 ; gastric juice, action of, on, 141 ; immunization 
with, 445, 447 ; leucocytes, relation of, to, 442 ; 
meningitis, in, 556 ; morphology of, 433 ; occurrence 
in body, 24, 434, 439 ; occurrence in nature, 434 ; 
phagocytosis of, 439 ; pneumonia, in, 502 ; resistance 
of, 434 ; symbiosis with Ameba coll. 6S7 ; toxin of 
Chantemesse, 447 ; vaccines, 444, 447 ; see Typhoid 
fever. 

Bacillus zerosis 407 

Bacterium coli commune; see Bacillus coli communis. 

Bactericidal serum, substance, etc. ; see Bacteriolysins. 

Bacteriolysins 245 

Absorption of, by bacteria, 251 ; composition of, 249 ; 
curative value of, 371, 375 ; endotoxins, action on, 
252, 372 ; group reaction with, 250 ; immunity, rela- 
tion of, to, 250 ; inactivation and reactivation of, 
248, 249 ; nature and selective action of, 246 ; origin 
of, from body cells, 147, 253 ; properties, general, 
245 ; prophylactic value of, 371 ; specificity of, 250 ; 
standardization of, 253 ; technic of testing, 254 ; 
therapeutic use of, 370 ; see Amboceptors and Com- 
plements. 

Bacteriolysis and bacteriolysin 245 

Bacteriolysis. 

Group reaction, 268 ; mechanism of, 260 ; Pfeiffer's 
phenomenon, 246 ; similarity to hemolysis, 250 ; see 
Bacteriolysins. 

Bacteriolytic enzymes, relation to immunity 172 

Bacteriotropic substances 371, 548 

Balanticlium coli, morphologv, occurrence and pathogen- 
icity 691, 692 

Balanticlium minutum 692 

Benzol ring ; use of, as an analogy in Ehrlich's theory. 
340. 

Bile. 

Bactericidal and antitoxic properties of, 142 ; immune 
agglutinins in, 209. 

Biologic test, 283 ; biologic test for species ; see Precipitins. 

"Black Death" ; see Plague. 

"Blackwater fever" in malaria 663 

Blastomycetic dermatitis ; see Oidiomycosis. 

Blastomycosis ; see Oidiomycosis. 

Blue pus 422 

Bocio urinarius 694 

Botulism 419-422 

Absorption of toxin, 421 ; antitoxin. 203, 422 ; im- 
munity, 422 ; infected meats, 420 ; phagocytosis. 



708 INDEX. 

l-A'.L 

»_••_•; prophylaxis, 422; susceptibility, 421 : -\ mj>- 
t'wns. 419: tissues affected by t"\in. 421; 
Hut m us botulinus. 

Bovine peel 26 

Bronchitis. 

in epidemic cerebrospinal meningitis, 559; meningo- 
coccus in. .'.:.:•: Mioroooocua catarrhalia in, 551, 
staphylococcus In 544; streptococcus In, 529. 

Capsolated bacilli 571, 572 

< larbuncle, staphylococcus In 5 I ■"•. S 1 1 

Card ia. hereditary susceptibility i<> 189 

CelJ receptors ; see Receptors. 

■ nus inti stinuiis. morphology and pathogenicity 
of 692, 693 

< Chancroid : see soft chancre. 

Chemicals In relation i-> antibody formation S42 

Chemotaxls i 16, 897, 315 

Chicken cholera, attenuation <>r microbe of 

Chlcken-poi i varlcells i 743, 744 

Chicken typhus or chlcken-pest 26 

Cholera 25, 169 180 

Accidental, In man. »7s: agglutination reaction, I s ": 
animals, Bosceptlblllty of, to, 174; antibodies, origin 
of, ::•_'«•. it:': antitoxic Berum, 480; bactericidal 
power of body fluids. »7 s ; "cholera carriers," 469, 
i.s : diagnosis, bacteriologtc, 480; epidemiology, 
■»7.:. 174, 176, 477 ; experimental. In man. i.s 
trie Juice, protective action <<i. 478; geographic dis- 
tribution "f. it.".; Immunity and susceptibility to, 
161, 169, 329, 178, 179; Infection atrium, 472; 
lesions. Intestinal, 475; effect of leucotoxlc serum on 
Infections, 298; mechanism "i" Intoxication, i . .". ; 
mixed Immunization In, 878, 489; phagocyte 
378, 319, 478. 479; phagolysls, 318; prophylaxis, 
362, 172, 17»'.: -■rum properties In, 211; sero- 
therapy, 374, 189; sources of Infection and trans- 
mission, 17l: 17 \ -. vaccines and vaccination, 166, 

4 77. 478 : see I i'"i" ChoU m . 

Cholesterln, neutralising action on tetanolysin 294 

Chromophages 399 

Cladothrix, Infections with 634 

Clavelee (sheep-pox) 26, 743 

Co-agglutinlna 225 

Cobra-leclthid 275 

» !obra venom : Been Venoms. 

Coccidla, life cycle, morphology Bpore formation and 
pathogenecity, 694, 695. 

Coccidiosis 694, 695 

Cocddiutn big* minum 095 

<'<><■> iiiiutn cunicuU s. ovifortm 695 

Cocobacteria septica (Billroth) 515 

Coley's mixture 529 

Colle's law : see Syphilis. 

Colloids 242-244 

Complement. 

Absorption of. 259. 373; analysis of, -77 : decrease Of 
during disease. 374 ; diversion of. 272. 373, 374 ; 
inhibition of, 280 : isolation of. 255 : lecithin as a, 
274 : multiplicity of. 268. 354: origin of, 253, 310: 
neutralization of, by salts. 204, 270 ; receptors of 
second order, 351 ; resistance to heat, 249 ; solu- 
tions of 258 ; sources of, for bactericidal serums, 



'INDEX 769 

PAGE 

372, 373 ; specificity of, 266 ; structure of, 263 ; uni- 
city, theory of, 354 ; see Cytase. 

Complement deviation 279-291 J- 

Antibody of, 281 ; as biologic test, 283 ; in sypbilis, 
284 ; in other diseases, 284 ; nature of, 281 ; relation 
of amboceptor to, 283 ; uses of, 283. 
Complementophilous haptophore ; see Haptophore. 

Complementoid 264, 353 

Complementoid-Verstbpfung 264 

Conjunctivitis. 

B. inflenzce, in, 566, 567 ; diphtheritic, 400 ; meningo- 
coccus in, 559 ; pneumococcus in, 514, 515 ; staphy- 
lococcus in, 544. 

Connective tissue, rOle of, in inflammation 144, 148 

Contact infection 19 

Contagion and contagiousness 18 

Contagious disease, definition 18 

Copula of Miiller, synonyms for 263 

Cow pox 738, 743 

Crotin 218, 427 

Cryptogenetic infections 34 

Crystalloids, properties of 243 

Culix fatigans 728 

Culex pipiens, in transmission of malaria of birds. ..... 670 

Curative injections 364 

Cyclaster scarlatinalis 744 

See Scarlet fever. 

Cystomonas urinarius 694 

Cytase 308, 311, 312 

See Complement. 

Cytophagic index 332 

Cytoryctes variolas s. vaccinas 731 

Conjugation, 732, 733 ; cytoplasmic stages, 732 ; life 
history of, 732-734 ; nuclear stages, 733 ; small-pox, 
in, 731 ; vaccinia, in, 733. 

Cytotoxins (Cytolysins) 160. 173, 292, 305 

Activity, determination of, 294 ; amboceptors in, 295 ; 
antileukotoxin, 299 ; antinephrotoxin, 300 ; anti- 
spermotoxin, 296 ; autocytotoxins, 293, 294 ; auto- 
nephrotoxin, 299 ; autospermotoxin, 296 ; ciliated 
epithelium, cytotoxin for, 294 ; complements in, 295 ; 
for malignant tumors, 297 ; hepatotoxins, 301 ; in- 
fections, effect of leukotoxins on, 298 ; leukotoxin, 
297 ; nephrotoxin, 299 ; neurotoxins, 301 ; origin, 
310 ; of venoms, 429 ; pancreotoxin, 304 ; specificity, 
lack of, 303 ; spermotoxin, 295 ; structure of, 295 ; 
syncytiotoxin, 301 ; technic of production, 294 ; thy- 
rotoxic 303 ; utility, theoretical, 292, 298. 
Cytolysins ; see Cytotoxins. 

Dacryocystitis, pneumococcus in 514 

Daphnia, phagocytosis of 313 

Dengue fever 728, 729 

Characteristics of, 734 ; contagiousness of, 728, 729 ; 
Culex fatigans in transmission of, 728 ; etiology, 
728 ; occurrence, 728 ; "plasmeba" in, 728 ; recur- 
rences and relapses, 729 ; susceptibility to, 729 ; 
transmission, 728. 

Desmon 263 

Deuterotoxin 196, 353 

Diphtheria 25, 28, 398-408, 

Agglutination reaction, 407 ; bacilli, localization of, 
401 ; conjunctivitis, diphtheritic, 400 ; forms of, 
400 ; immunity and susceptibility, 161, 172, 402, 



i\iu:\ 



108; infection atria, 400; latent, -i<»<>: leucocytes 
in. 403; mixed Infections in. 81, 816, 101, 524; 

paralysis. Influence Of antitoxin mi. 406 ; predis 
103; pneumonia in. 510; prophylaxis, 
404; peeudodlphthena bacilli in. 4< >7 ; recurrences, 
161, 404; Beptic, 4<»l' ■ serotherapy, 369, 404; 
sources of Infection, 399, 100; tissues injured by 
toxin, 401; transmission, 400; Bee Bacillus diph- 
tin rim, 
Diplococcus Intracellularis meningitidis; Bee Micrococcus 
tneningitidis. 

• rrux JitHlUll'itliir .".Ml. 515 

Agglutination of, 504; alveolar abscess, in. 514; ani- 
mals, susceptibility of, 504; conjunctivitis, 514, 
515; dacryocystitis, 514; discovery of, 502; endo- 
toxins. 504; 'Ht' ritis. .".it lutination, 
514; Immunisation with. 510. 511, 512; Influenaa, 

567; meningitis, 514, 515. 556; morpho 
Btalnlng, ami cultivation, 502, 508; neurotoxic 
strains <>f. 504 ; occurrence in blood, 509; occur- 
rence, normal, 505 : otitis media, in. 514, 515; peri- 
tonitis, iii. 514, .".1:.: phagocytosis of, 505, 111 j 
pneumonia, In, 502. 515; pneumotoxin, 504; pulmo- 
nary hemorrhage, In, 510; resemblance t<» strepto- 
coccus, 503: resistance, 503; rhinitis, In, 514; sep- 
ticemia. 514 deer, 514, 515; tuberculosis, 
in. 593; virulence, 505; virulence, Increase <>f. 508; 
1 neumonia. 

Dlpl tccue us) in rheumatic fever 525 

Dourine ; see Trypanosomiasis In animals. 

Droplet Infection 400 

in diphtheria, 400; In Influenaa, 567; In tuberculo- 
sis 582. 

Dust Infection 400 

in diphtheria, 400; In Influenaa, 567 ; in tuberculosis, 
581, 582 : In typhoid fever, 136 

Dysentery, acute epidemic 23, 25, 453-459 

Agglutination reaction, 459; amis, .rums, properties 
of, 458; bacilli, dissemination <>f. by stools. 157 ; 
bacilli, distribution of, In the body, 455; chronic, 
153; 4 .17 : immunity ami BUSCeptlbllity, 169, 457. 
158; Incubation period, 453; institutions, occurrence 
in. 4.1T: Intestinal lesions In, 455; occurrence of, 
45S : predisposing causes of, 457 : prophylaxis. 457 ; 
therapy, 458; Bummer diarrheas of infants. 454; 
transmission, 457; vaccination. 4.1^: see BaciUus 

ilrisrntrriiT. 

East Coast fever 70 

Eclampsia, relation of syncytiotoxin to 301 

Eczema, relation of staphylococcus to 543, 544 

Eel serum, antitoxin for 203 

Ehrlich's parital saturation method 193, 353 

Ehrlich's "side-chain" theory. Sec "Side-chain" theory 

of Ehrlich. 
Endocarditis. 

Colon bacillus in. 467 ; gonorrheal, 553 ; pneumococ- 

cus in, 509, 514 ; staphylococcus in, 525, 544 ; 

streptococcus in, 520, 524. 

Encephalitis, in epidemic cerebrospinal meningitis 559 

Endocomplement 274, 430 

Endotheliotoxin, of venom 428 



INDEX. 771 

T, ^I * • PAGE 

Endotoxins 4D,-, 

Anthrax bacillus, 495; Bacillus pyocyaneus. 423,424*; 
bacteria containing, 370, 375 ; cholera vibrio, 475 ; 
diseases associated with, 433 ; dysentery bacillus, 
456 ; failure of bactericidal serums to neutralize, 
371 ; glanders bacillus, 624 ; of gonococcus, 552 ; 
leprosy bacillus, 621 ; liberation of, bv bacteriolytic 
serums, 252, 372 ; meningococcus, 558 ; paratyphoid 
bacillus, 452 ; plague bacillus, 484 ; staphylococcus, 
425, 540 ; streptococcus, 425, 518 ; tubercle bacillus, 
577 ; typhoid bacillus, 435. 
Enteritis. 

Ameba coli in ; see Amebic dysentery ; Balantilium 
coli in, 691 ; Cercomanas intestinalis in, 692 ; colon 
bacillus in, 468 ; pneumococcus in, 514 ; staphylo- 
coccus in, 544 ; streptococcus in, 520, 521, 523 ; 
Trichomonas intestinalis in, 693. 

Enzymes, bacteriolytic, relation to immunity 172 

Enzymes, intracellular 306 

Epilepsy, cytotoxin in 304 

Epithelioma contagiosum of fowls 26 

Epitoxoids 194 

Erysipelas 521 

Effect on tumors, 529 ; experimental production of, by 
streptococcus, 521; in course of tuberculosis, 522; 
recurrence of, 161 ; staphylococcus in, 521 ; strep- 
tococci in, 516, 520. 

Etiology, infectious 22 

Etiology, unknown ' 26, 697 

Excretions, infectivity of 37 

Exhaustion, toxin of 304 

Farcin du bozuf 634 

Farcy, see Glanders 25 

Fermentation, early studies on 4 

Fibrin, mechanical value of in inflammation 148 

Fixator, synonyms for 263 

See Amboceptors. 

Filiaria perstans 674 

Fish, B. enteritidis in, poisonous 462 

Fish poisons, antitoxins for 203 

Fleas, in the transmission of plague 486, 487 

Flies, as carriers of typhoid fever. 436 

Fly transmission 65 

Fomites 715 

Food-substances. 

Fixation of, by amboceptors, 352 ; manner of union 
with cells, 341 ; non-formation of antibodies for, 343. 

Foot-and-mouth disease 26, 27 

Fowls, epithelioma contagiosum of 26 

Fusiform bacilli ; see Noma. 

"Gambian Fever ;" see Trypanosomatic Fever. 

Gastric juice. 

Protective role of, 141, 478, 494. 

Gelatinase 538 

German measles (Rotheln) 750 

Glanders (Farcy) 25, 138, 623-629 

Animals, susceptibility of, 623 ; bacilli, distribution of 
in the body, 625 ; connective tissue development in, 
626 ; diagnosis, bacteriologic, 628 ; healing proc- 
esses in, 627 ; immunity, 627 ; infection atria. 625, 
626 ; mallein in diagnosis of, 628 ; organs involved, 
627 : phagocytosis, 627 ; serotherapy, 628 ; tissue 
reactions, 626 ; see Bacillus mallei. 



7 7 2 INDEX. 

i a. .i; 

Olossina palpaMs in transmission "' Bleeping Blckness... *'>7."» 

Gonococcas; Bee Micrococcus gonorrhea. 

Gonorrhea 25, 161, 551 556 

Acnte ami chronic, 554, 555; complications ol 
:.:.»: Immunity. 161, 554, 555; ophthalmia In, 558; 
phagocytosis, 552, 557; reinfection, 554, 555; super- 
Infection, 555; susceptibility of different tissues to, 
553; urethral changes, 554; see Micrococcus gon- 

"ii In u . 

Gonotozlo 553 

Grass Bacilli 614 

Qregarina lindemanni; see Sarcosporidla. 

Group agglutination 224, - - J7. it'.'. 452, 463, 512, 536 

Gruber-wldal reaction; see Agglutination. 

Hair-, phagocytosis "i" pigment i>> cbromaphagei .".'»'.» 

Hal teri alum. 

Impregnation of parasites, 654; In malaria <>f birds, 
669. 

Haptophores 192, 341, 843, 851 

Haptophorous groups ; see l laptophoi 

Hauptaaglutinlns 226 

Hay fever 125-427 

Antitoxin (pollantln), -"». 126; pollen as cause of, 
125 : toxin of, 125 

Hanging-drop preparation 212 

Hemagglutinins. 
< n plants, 218; of Berums, 218; of venom, 128. 

Hcmogiobinurtc fever, In malaria •'••"..". 

Hemoij 
Animal, ii's. 132; bacterial, 346; cobra lecithld, 275, 
130; colloids as, 276: experimental value of, 256; 
from organ extracts, 310; Immune, In scrums, 178, 
256; Intraleucocytlc, 810; normal, In Berums, 160; 
pyocyanolysin, 424; serum hemolysins, structure of, 
staphylococcus, Bee Btapbylolysln ; streptococ- 
cus, Bee Streptocolysin ; tetanolysln, 113; venom of, 
2£ 
Hemolysis ; « e Hemolysins. 
Hemolyl Ic experiments. 

Technic of, 256; value of, In Btudy of immunity. 256 

Hemorrhagic septicemia group of bacteria i v _ 

Hemorrhagin 273, 128 

Hemotoxins 178 

Hepatotoxins 301 

I [eredltary Infection Gl 

Heterologous scrum 208 

Homologous scrum 208 

"Horror autotoxicus" 305 

Horsepoz 743 

Hydrophobia 25, <;07-710 

Animals, in. 700, 7m : diagnosis, in dogs, 702, 703; 
extension through nerves, 704; fixed virus of, 700; 
immunity, character of, 710 ; immunization, mixed, 
.I"; incubation period. 702, 704. 705; micro-organ- 
isms found in, 697 ; Negri bodies, 697, 698 ; Pas- 
teur treatment, 705. 710; prophylaxis of, 704, 710; 
specific lesions. 703 ; street virus of, 700 ; trans- 
mission of, 701 ; toxin, question of, 698 ; vaccina- 
tion, 6, 7, 707 ; vaccina preparation of, 705, 706 ; 
virulence for man, 700, 704, 707 ; virulence, in- 
crease and decrease of, by passage, 700 ; virus, 
attenuation of. 166, 363. 698, 706-710 ; virus de 
rue, 700 ; virus, distribution and excretion of, 



INDEX. 773 

PAGE 

700 ; virus, filterability of, 27, 698 ; virus fixe, 
700, 705 ; virus, resistance of, 699. 

Ichthyosismus 420 

Ichthyotoxin 432 

Immunity. 

Absolute, 135 ; acquired, 129, 161-175 ; active, 134, 
161, 168 ; antibacterial, 132, 149, 154, 355 ; anti- 
toxic, 132, 154, 155, 354; definition of, 128; in 
families, 130 ; leucocytes, relation to ; see Phago- 
cytosis ; natural, 129, 137-160 ; early theories of, 
1 ; passive, 134, 169 ; relative, 134 ; theories of, 7, 
12 ; types of, 135 ; see Antitoxins, Bacteriolysins, 
Phagocytosis and the individual diseases. 
Immunization. 

Active, a curative measure, 364 ; active, for prophyl- 
axis, 376 ; classification of methods, 362 ; choice 
of animals for, 373 ; mixed, 364, 378 ; passive, as 
curative measure, 364 ; passive, in prophylaxsis, 
364 ; with tissue cells, 294 ; with toxins, 10. 
Impetigo contagiosa. 
Staphylococcus in, 520 ; streptococcus in, 520. 

Incubation period 354 

Infection 

"Air borne," 19 ; atrium of, 19, 137, 141 ; carriers, 
39 ; contact by, 19 ; mixed, 26, 30, 31, 227 ; - see 
individual diseases ; "water borne," 19 ; infectious 
agents, classification of, 21. 

Infectiousness and contagiousness 18 

Infectivity 88 

Infestation 14 

Inflammation. 

Antagonism of, to infections, 148 ; chemotaxis, 146 ; 
connective tissue, inflammatory role of, 143, 148 ; 
fibrin, influence of, 148 ; injurious effects of, 143, 
144 ; leucocytes in, 145, 147 ; nature of, 143 ; organi- 
zation in, 147 ; phagocytosis in, 145-147 ; plasma, 
influence of, 147 ; relation of, to virulence of bac- 
teria, 144, 145 ; role of, in immunity and resist- 
ance, 143 ; variations in intensity, 144-146. 

Influenza 25, 563-569 

Conjunctivitis in, 567 ; chronic, 567 ; contagiousness 
of, 563 ; epidemics of, 563 ; immunity, 568 ; infec- 
tion atrium, 567 ; intestinal, 566 ; intoxication, 
566 ; meningitis in, 566, 567 ; mixed and secondary 
infections in, 567 ; otitis media in, 566, 567 ; peri- 
tonitis in, 566, 567 ; phagocytosis in, 566 ; pneumonia 
during, 510, 566 ; prophylaxis, 568 ; recurrence of, 
161, 568 ; susceptibility, 568 ; transmission of, 567 ; 
tuberculosis during, 567 ; see Bacillus influenzas. 
Insects. 

In transmission, 67 ; incubation in, 81. 

"Intestinal group" of bacteria 434 

Intoxication 96 

Iso-agglutinins 218 

Isoprecipitins 236 

Kala-Azar 696 

Lactoserum 235, 240 

Lamblia intestinalis 694 

Leischman Donovan Bodies : See Kala-Azar. 

"Leistungskern" 209, 339 

Lecithin as endocomplement 274 

"Leprolin" 621 



77 1 INDEX, 

PAOt 

Leprosy 25, 615-623 

Animals, Insusceptibility of, to, 618; contagious 
6Y, 616; distribution of bacilli In the body, 620: 
extension and occurrence <>t\ 615; tish. relation of 
to, '".l:*: Infection stria, 619: Intercurrent Infec- 
tions, 621 : phagocytosis in. 621, 622; potassium 
lodld in treatment of, 621; prophylaxis, 622; pro- 
tective factors in. 622; Berotnerapy of, 623: ^p- >n - 
taneons disappearance <>(. 621: susceptibility to, 
''.l'l 1 : transmission of, 618; tubercular, 621; 
/;<;. Him /( /-/(/ . 

Leptothrlx, Infections by 634 

l.i ptothrix bucoalis 634 

Leptothris vaginalis •'..".» 

178, 846, 539, :.I7. 540 

Antitoxin tor 539; Influence on phagocytosis, 589. 

Absorption <■!' toxins by, 321 : complement in. 269; 
formation of precipitins by, 286; Immunity, illa- 
tion to, :;«n; 323 : in inflammations, I 15 ; phago- 
cytic properties of 145, 146, 147; Bee also individ- 
ual die 

Leucocytlc exudates, bactericidal action of 546 

"Loop." standard _ 215 

Leucotoxlc serum l**.»7. :j;»s 

ICOtOXiC S- •nun. 
••Lumpy jaw :" >-.•.• Aeiinom\ i 

Lupus, Influence of Btrepfe ecus on 

Lymphangitis, streptococcus In 520 522 

Lymphatotoxln ; see Leucotoxlc Berum. 

Macrocj tase 

-i 

Macrophages 146, 298, 308, 31 I 

Madura fool : see Mycetoma. 

Mai <h oaderat; see Trypanosomiasis In animals. 

Malaria 654-670 

.im ivo autumnal. 655; estivo-autumnal, parasite of; 
Plasmodium pratcow; anemia in. 690; "black- 
water" fever in. 663 : cachexia in. <;•;:: ; cerebral 
symptoms, 668; epidemiology of, 664; etiology of, 
654 : fever, relation of to developmental cycles 
of parasites, 660; bemogloblnuric fever In, •'.<;::: 
immunity, acquired, 667, 668; Incubation period, 
659; intestinal symptoms. f,t;.'{ ; malanemia in, G90 ; 
methylene blue in. 661 ; mixed infections, G62 ; mos- 
quitoes, transmissions l>v. 654 : neuralgia in, 003; par- 
asites, localisation of, 663 : prophylaxis of, 000, 007 ; 
quartan. 655; quartan, parasites of ; see Plasmodium 
malaritr. quinin in prophvlaxis and treatment of. 
003. 666, 667 ; quotidian, f.02 ; relation of clinical 
svmptoms to developmental cycles of parasites. 
003 ; susceptibility to. GOT ; tertian. 055 ; tertian, 
parasite or; see Plasmodium rivax; toxins. 601: 
transmission ; see Anopheles ; see Plasmodium of 
malaria. 

Malaria of birds, halteridium in: proteosoma in 609 

Malignant pustule: see "Anthrax." 

Mallcin 364, 625, 628 

Malta Fever 498-500 

Accidental infections. 500 ; agglutination reaction in, 
499 ; difference from typhoid fever. 499 ; distribu- 
tion of bacillus in body. 499, 500 : immunity, 500 ; 
occurrence. 498 ; serum, properties of. 499 ; sero- 



INDEX. 775 

PAGE 

therapy, 500 ; transmission, 500 ; see Bacillus meli- 
tensis. 

Measles 747-750 

Complications and sequelae, 749 ; contagiousness of, 
748 ; immunity and susceptibility, 749 ; leprosy, in- 
fluence on, 621 ; leucocytes in, 750 ; Micrococcus 
catarrhalis in, 550 ; micro-organisms in, 747 ; pro- 
phylaxis, 749 ; racial immunization, 749 ; resistance 
of virus, 749 ; recurrences, 749 ; serotherapy, 750 ; 
virus, distribution of, 748. 

Meat poisoning. 

Bacillus ootulinus in, 419 : Bacillus enteritidis in, 
459-463 ; Bacillus paratyphosus in, 450 ; relation of 
ptomaines to, 460. 

Mediterranean fever ; see Malta fever. 

Meningitis. 

B. pneumonia? in, 572 ; colon bacillus in, 467 ; in influ- 
enza, 566 ; micro-organisms causing, 319, 556 ; 
pneumococcus in, 509, 514 ; secondary, 522 ; strep- 
tococcus in, 520, 522, 524 ; tuberculous, 587. 

Meningitis, epidemic cerebrospinal 556-563 

Agglutination test, 560 ; cerebrospinal character of, 
559 ; complications, 559 ; contagiousness of, 559 ; 
immunity, acquired, 560 ; lumbar puncture for diag- 
nosis, 559 ; metastatic infections, 559 ; mixed and 
secondary infections in, 559 ; prophylaxis of, 560 ; 
secondary to rhinitis, 558 ; serum properties of, 
560 ; susceptibility to, 560 ; transmission of, 559 ; 
see Micrococcus meningitidis. 

Meningococcus ; see Micrococcus meningitidis. 

Metchnikoff's theory ; see Phagocytosis. 

Methylene blue, effect of, on malarial parasites 661 

Microbic specificity 4 

Micrococcus catarrhalis 550, 551 

Animals, susceptibility of, to, 551 ; bronchitis, in, 551, 
559 ; measles in, 550 ; occurrence in respiratory 
passages, 550 ; occurrence under normal conditions, 
551 ; pneumonia, in, 502, 510, 551, 560 ; resemblance 
to meningococcus, 560 ; scarlet fever in, 550 ; 
whooping-cough, in, 550. 

Micrococcus gonorrheal (gonococcus) 383 

Antiserum for, 555 ; cultivation of, 551 ; discovery of, 

551 ; endotoxin of, 552 ; gonotoxin, 553 ; immuniza- 
tion with, 555 ; infections with, 551, 555 ; mor- 
phology, 551 ; phagocytosis of 552 ; resistance of, 

552 ; toxin, soluble, 555 ; see Gonorrhea. 

Micrococcus hematodes 541 

Micrococcus melitensis ; see Bacillus melitensis. 
Micrococcus meningitidis (Diplococcus intracellularis 

meningitidis, or the meningococcus) 25, 556-563 

Agglutination of, 560 ; animals, susceptibility of, 557 ; 
antiserum, properties of, 561 ; bronchitis, in, 559 ; 
conjunctivitis in, 559 ; cultivation, 557 ; discovery, 
556 ; endotoxin, 558 ; excretion of, 559 ; immuniza- 
tion with, 560 ; morphology, 557 ; pneumonia, in, 
559 ; resemblance to gonococcus, 557 ; resemblance 
to Micrococcus catarrhalis , 559 ; resistance, 557 ; 
rhinitis in, 559 ; virulence, 558 ; see Meningitis, 
epidemic cerebrospinal. 

Microcytase 308-319 

Micro-organisms. 

Acquired resistance of, 116 ; early belief in, 2 ; excre- 
tion of, 37 ; recognition of, 3 ; sources of, in earth, 



778 INDEX. 

41; in miter food, 42; In Inflects, 44: In man. 47; 
In air. 40; ultramlcroscoplc, 21; liability of, 55. 

aficroparasltes 21 

aficrophagee 146, 308, 31 t. 320 

Mioro§poron Beptioum I Debs) 515 

Milk bacilli 614 

Mitagglutinin 225 

"Momadinin" ..i" Klebs 525 

afucor 641 

Muini's (epidemic parotitis) '55 

Mycetoma 638 

Nagana ; Bee Trypanosomiasis in animals 680 

Natural Immunity; Bee Immunity. 

\ gatlve phase Following vaccinations 377 

Negri bodl< - ; Bee I lydrophobla. 

Nephrotoxic ' 299, 300 

309 

Neurotoxin of serums •"."] 

Neurotoxin of venom 178, 128 

Noma ■ 

Oldla 21, 25 

l Oidiomycosis 635 841 

in animals, 640; cutaneous, 635; Infection atria, 
organisms of, <..".•".; resemblance to tuberculosis, 
mic, 635; thrush, 

Oldlum 635 

itinatlon, Immunisation and phagocytosis, 640. 

Oidium albU ant 639 

Oidium ('" < idiodi t *',:{7 

Old age. fi£etchnlkoff*s theory of 298 

< Ophthalmia. 

Cytotoxinc In, .".<•»: gonorrheal, 553. 

ms 824 338 

distinct antibodies, .".'J'.' : Immune opsonins, 328; 
Interaction with leucoi 2 normal opsonins, 

:;::<•; opsonic Index, 325; proof of action <>f. 324; 
relation to Immunity, 330; relation to vlrulin, 
specificity i 

I Opsonocytophagic Index 332 

otitis media. 

/;. infliK >i;n in. .",•;•;. 567; pnemnoeoccus in. 514; 
staphylococcus In, 544 : Btreptococcus In, 524 ; tuber- 
culous, 587. 

Oxytuberculln 580 

Ozena 572 

Pancreatic Juice, action on toxins 142 

Pancreotoxln 304 

"Paracolon*' bacilli 450 

Parasites, pathogenic 13, 21 

Parasitism 1 1 3 

Paratyphoid Fever 449- 153 

Agglutination reaction In, 4.">2 : blood cultures In, 4.".:;: 
characteristics of the disease, 451 ; endotoxin of 
bacilli, 452; epidemiology of, 45o; as meat poison- 
ing. 450 : occurrence of bacilli in the body, 451 ; 
properties of serum. 452 : prophylaxis. 45-2 ; trans- 
mission. 450, 451: see Bacillus* paratyphosus. 
Parotitis, epidemic ; see Mumps. 

Passage 91 

Passive immunity ; see Immunity. 
Pasteur treatment ; see Hydrophobia. 

Pathogenesis * 88 

Peripneumonia of cattle 2G, 27 



INDEX. 777 

PAGE 

Periostitis albuminosa ."4.", 

Periostitis, staphylococcus in r.4.". 

Peritonitis. 

Colon bacillus in, 468 ; by influenza bacillus. 566, 
567 ; pneumococcus in, 513, 514 ; staphylococcus in, 
544 ; streptococcus in, 520. 523 ; tuberculous, 587. 
Pertussis ; see Whooping-cough. 

Pfeiffer's phenomenon 210, 246 

In ^identifying the vibrio of cholera, 471 ; rule of 
leucocytes in, 318. 
Phagocytic (Metchnikoff's) theory of immunity ... .306, 331 
Comparison of, with the side-chain theory of Ehrlich, 
356, 357 ; see Phagocytosis. 

Phagocytosis 9, 146, 306-331, 354 

In active immunity, 168, 169, 324, 325 ; chemotaxis 
in, 307, 315 ; fixators, influence of, 320 ; in inflam- 
mations, 145 ; intestinal, 143, 307 ; intravascular, 
318 ; leucocidin, influence of, 539 ; in nutrition, 
302 ; in passive immunity, 169 ; relation of to viru- 
lence of bacteria, 314, 317 ; in resorption, 308 ; 
serum, influence of, 317 ; in vitro, 153 ; see under 
the individual micro-organisms and diseases ; see 
Opsonins. 

Phagolysis 311, 312, 318, 320 

Phallin 428 

Phrynolysin 431 

Phytoprecipitins 235 

Placental transmission : 60 

Plagiomonas urinaria 694 

Plague 25, 481-492 

Agglutination reaction, 492 ; animals, susceptibility of, 
484 ; contagiousness, 487 ; diagnosis, bacteriologic 
488 ; dissemination of bacillus by urine, feces, 
sputum, 487 ; epidemiology. 487, 488 ; foci of, 485 ; 
immunity, 161, 169, 489, 490; infection atria, 487; 
mixed immunization in, 489 ; mixed infection in, 
488 ; occurrence, 481 ; houses, 487 ; prophylaxis, 
488 ; in rats, 486 ; serum therapy, 490, 491 ; trans- 
mission by fleas, 486 ; transmission from rat to man, 
486, 487 ; vaccination, 166, 362, 389 ; vaccines, 489, 
490 ; see Bacillus pestis. 

Plasmin of Buchner 179. 363 

Plasmodia of malaria 25, 654 

Anopheles mosquito as host of, 24, 655 ; asexual 
cycle, 656 ; development in anopheles, 656 ; devel- 
opment in man, 655 ; discovery of, 654 ; flagella of. 
654 ; macrogamete, 656 ; mcrozoites. 656 ; methylene 
blue, effect of, 661 ; microgamete, 656 ; niicrogame- 
tocyte, 656 ; oocyst, 657 ; ookinet, 657 ; schizogony. 
656, 660 ; sexual cycle, 656 ; species of, 655 ; sperma- 
tozoites, 654 ; sporocyte, 656 ; sporogony, 657 ; 
sporozoites, 657 ; see Malaria. 

Plasmodium malaria; 655 

Relation to clinical symptoms, 659 ; sexual and asex- 
ual cycles of, 656 ; virulence, 660. 

Plasmodium prwcox 655 

Relation to clinical symptoms, 659 ; sexual and asex- 
ual cycles of, 658 ; virulence, 660. 

Plasmodium vivax 655 

Asexual cycle of, 650 ; relation of to clinical symp- 
toms, 659 ; sexual cycle of, 656 ; virulence, 660. 
Pneumococcus ; see Diplococcus pneumonia. 



77- INDEX. 

I'm u iiH >iii;i 501, 513 

itlnatioo reaction, 512; /;. pneumonia In, ~>~- ; 
bacteria causing, 501, 502; causes, predisposing, 
508; complications, 509, 510, 513; contagiousness, 
507; Immunity and Busceptiblllty, 161. 510; Infec- 
tion atrium and method oi Infection, 505; Lnfluensa 
bacillus in. 566; leucocytes, 511; metastatic Infec- 
tion-. 518; phagocytosis, 511; meningococcus in. 
559; Micrococcus catarrhaHs in. 551. 559; mixed 
Infections in. 510; polyvalent Berum tor, :>\-\ pro- 
phylaxis, ."in; recurrences, 510; Roemer's serum, 
512: Berum properties. 510; serotherapy, 511, 512; 
staphylococcus in. 544; Btreptococcus in, 520, 521, 
522; vaccination, 510; Bee uiplococcus pneumonia 
ami other bacteria enumerated on page 502. 

Pneumotoxin 504 

PoliomyeiltlB (epidemic) 756 758 

in — mlnatlon. 758; experimentally produced, 757 : 
micro-organisms In, 757; virus distribution of, 757, 
Pollantln 126 

\ ' bay fever, 425; antitoxin for, 126. 

Polyceptors ' 269 

Polyvalent serums. 
For pneumococcus, 512; for staphylococcus, 550; for 
streptococcus, 376 

"Positive phase" following vaccination 877 

Post mortem Invasion 461 

Precipitate 235, 240, 24] 

Precipitation reaction 280, 234 

Agglutination, relation t". 280; as clinical reaction, 
_•:; t : with colloids and electrolytes, 244; forensic 
us.. i,f. it}, I'll: precipitation, l^ i- < • » j t • reaction, 
240, 241; meats, differentiation <>r. 242; physical 
chemistry in the study of, 2 i t ; specific Inhibition. 
237; technic, 241; use of in Btudymg reactions of 
Immunity, 350. 

Precipitins .' 284 244 

Antipreclpltins, 238; autopreclpitins, 236; bacterial, 
17}. 234, •"•77. 479; formation of, 236; Isopreclpi- 
tins. L-::*; ; lactoserum, 235; phytoprecipitins, 235; 
stance to ferments, heat, etc., 237; Berum pre- 
cipitins, Immune, 174; Berum precipitins, normal, 
160; structure of, 237; soOprecfpltins, 235. 

Precipitinogens 235 

Precipitoids 238 

Pregnancy, serum diagnosis 302 

Preparator 263 

Proajrplutinoids 223 

Prophylactic injections, classification of methods 36JJ 

Protective inoculation ; see Vaccination. 

Proteins 304 

Proteosoma in malaria of birds 669 

Prototoxin 190. :;.":: 

Protoxoids 106, 353 

Protozoa, infections with 654, 695 

Pseudodiphtheria bacilli 407, 591 

Pseudoinfluenza bacilli 564 

Pseudotuberculosis of animals 614 

Ptomains in meat 460 

Pyocyanase 172, 423 

Tyocyanin 423 



INDEX. 779 

PAGE 

Pyocyanolysin 424 

Pyroplasma bovis ; see Texas fever. 

Pyroplasma Jiominis ; see Spotted Fever. 

Pyroplasmas, inheritance of 77 

Pyroplasmosis ; see Spotted fever and Texas fever. 

Rabies, See Hyrophobia. 

Radium, effect on venom 431 

Rats in epidemics of plague 486, 487 

Rattlesnake venom. 

Antiserum for, 431 ; immunization with, 363. 

Ray fungus ; see Actinomyces 486, 487 

Receptors. 

Bacterial, 267 ; function of, 156, 200, 201 ; immunity, 
relation to, 343 ; loss of, as cause of immunity, 
403 ; multiplicity of, 200, 352 ; new formation of, 
343, 349, 351 ; nutrition, relation to, 339 ; of first 
order, 203, 344, 351 ; of second order, 228, 347, 
351, 353 ; of the third order, 265, 347, 351 ; syno- 
nym for side chain, 341 ; tetanophile receptors of 
nervous tissue, 415 ; types of, 351 ; see different 
antibodies. Recrudescences, 101 ; recurrences, 101. 

Relapsing fever 25, 642-646 

Agglutination test, 645 ; immunity and susceptibility, 
644, 645 ; organism of, see Spirochetes obermeieri; 
phagocytosis in, 644 ; prophylaxis, 644 ; serum prop- 
erties, 645 ; serotherapy, 645 ; transmission of by 
bedbugs, 643. 

Resistance, natural ; see Immunity, natural. 

Resorption. 

Of foreign cells, 309 ; of native cells, 308. 

Rheumatic fever 525-527 

Agonal invasions in, 525 ; antistreptococcus serum in, 
535 ; bacillus of Achalme in, 525 ; diplococcus 
(streptococcus) in, 526; experimental, 525, 526; 
micro-organisms found in lesions, 525 ; staphylococ- 
cus in, 525 ; streptococcus in, 520, 525, 526 ; 
Zymotosis translucens, 525. 

Rhinitis. 

Meningococcus in, 559 ; pneumococcus in, 514 ; pri- 
mary to meningitis, 558 ; staphylococcus in, 544 ; 
Rhinitis fibrinosa, 400. 

Rhinoscleroma 572 

Ricin 21, 427 

Antiricin, 174 ; Ehrlich's use of iu studying nature of 
antitoxic action, 345, 346 ; hemagglutinin in, 218. 

Robin 427 

Rotheln, see German measles. 

Saccharomycosis hominis 635 

Salamander poison, antitoxin for 203 

Saprophytes 13 

In tetanus 411 

Sarcocystitis hominis; see Sarcosporidia. 

Sarcosporidia. 

Morphology, occurrence and proliferation, 690, 691 ; 
Sarcocystis hominis, 691. 

Scarlatina ; see Searlet fever. 

Scarlet fever (scarlatina) 744-747 

Agglutination of streptococci by serum, 536, 537 ; con- 
tagiousness, 745; Cyclaster scarlatinalis in, 744; 
Diplococcus scarlatince, 26 ; leucocytes in, 746 ; 
Micrococcus catarrhalis, 550 ; micro-organisms in, 
745 ; prophylaxis, 745 ; protozoa in, 25, 744 ; re- 



780 INDEX. 

PAOI 

slstance ol virus, 7i.~; Berotherapy, 7»7; strepto- 
coccus in. 31, 316, 520, 521, 523, 527, 744; Strep- 
tococcus scarlatina, 527 \ Immunity and Busceptl- 
blllty, 161. 746; sero-therapy (antlstreptococcus), 
533, 53 i. 7i.; i ransmission, ■ 45. 

Scorpion, toxin and antitoxin 203, 482 

Sensitization 259 

Serpent ulcer. 

Pneumococcus In, 514, 515; treatment wiih antl 
pneumococcua serum (Koemer), 515. 

s.'niiu ,ij>, aae 395 

S.-rums. purity of 189, 365 

Serotherapy, principles ol 362-380 

Antitoxins, 365, 370; bactericidal Berums, 370, 376; 
classification <>i" methods, 362; curative injections, 
364, 367, 371 : prophylactic Injections, 362, 370, 
373 : see also under the different diseases. 
Sheep-pox ; Bee » llavelee. 

Side-chain theory of Bhrllch 339 361 

Amboceptor formation, 264 ; agglutinin formation, 228 : 
antitoxin formation, 199, 202 ; applied to cell nutrition, 
339; as applied to Immunity, 343; chemical pro- 
s, 191, 344, 348. 351; complements, 268, 354; 
of, 344 : baptophores, 341 : ••/.< Is- 
tungekem" 389; Metchnikoffe phagocytic theory, 
comparison with, .".."-•'-. 361; precipitin formation, 

receptor proliferation, 349; receptors, typi 
351 : side chains, 389. 

Sleeping <;7:: 678 

Anatomic lei f6; bacteria In, 674; occurrence, 

674, 675; Bymptoms of, 675, 676: transmission of, 
675; Trypanosomatlc fever, relation to, 676, <"> .7 : 
trypanosomes In, 674; - • Trypanosomiasis. 

Small-pos 729 7 13 

Bacteria In I inversion Into vaccinia, 729, 

7.".n : cyclic nature of Bymptoms, 735; Cytoryctes 
variola >. vaccinia, !■'■ l : dissemination of virus, 
734; etiology, r30: fetal, 731; Immunity and sus- 
ceptibility, 164, 742; Incubation period, 7::.".: Infec- 
tion atrium, 7::i: Inoculation Into calves, T u*. > ; Jen- 
nerisation, 7::7 •. leucocytes In, 742 ; mixed (second- 
ary) Infections, 30, 7.".';: nonfiltrability of virus, 
7.".n; prophylaxis, 736; protozo5n-like bodies in. 26, 
r30; relation to vaccinia, 165, !-'■> : revaccination, 
74i». 741 ; sernm properties, 74l': transmission, 734 ; 
vaccination, 736; vaccine, contaminations of, 7:;!». 
74<i; vaccine, durability of. 739; virulence, varia- 
tions in. 7.':..: virus distribution in the bod v. 7:;.". 

Small-pox and vaccinia 729, 743 

Smegma bacilli 613 

Snake bites 4L'S. 431 

Soft chancre or chancroid .569-571 

In animals. 570; bacillus of, 570; immunity. .",71: 
independence, 569; infectiousness of, 569; phago- 
cytosis, 570, 571. 

Specific infections 9 

Specificity in transmission 86 

Spermophilua colwnbianus as host of Pyropla&ma hominis 721 

Spermotoxin 295, 296 

Spider poison, antitoxin for 203 

Spirocheta. 

Anserina. 053 : diseases due to. 642 : gallinarum, 653 ; 
pallida : see Syphilis ; pertenuis, 052 ; Theileri, 653. 



INDEX. 781 

PAGE 

Spirocheta obcrmeieri 25, 642 

Animals, susceptibility of, 643 ; antiserums, properties 
of, 644 ; distribution in the body, 643 ; morphology. 
642 ; occurrence in bedbugs, 643 ; phagocytosis of, 
644, 645 ; see Relapsing fever. 

Spotted fever 73, 720-725 

Immunity in, 725 ; maintenance of, 723 ; micro- 
organisms in, 724; pyroplasma hominis in, 720; 
transmission to man, 722 ; to other animals, 722 ; 
transmission by ticks, 721, 723. 

Staphylococcus pyogenes, or staphylococcus 537-550 

Agglutination, 206, 549 ; amyloid degeneration, 542 ; 
animals, susceptibility of, 543 ; antiserums, prop- 
erties, 547 ; bactericidal action of leucocytic exu- 
dates, 546 ; bacteriolysin, 546. 547 ; discovery, 516 ; 
endotoxin, 540 ; ferments of, 538 ; hemolytic action, 

538, 539 ; immunity, 316. 546, 547 ; leucocidin, 

539, 547, 549 : leucocytes in infections, 545, 546 ; 
leucotactic substance, 542 ; mixed infections, 545 ; 
morphology, 537 ; necrotizing substance, 542 ; path- 
ogenic powers, 139, 501, 510, 520, 525, 543, 544, 
556 ; opsonins in phagocytosis of, 549 ; phagocy- 
tosis, 545, 546, 548 ; pigment formation, 541 ; poly- 
valent serum, 550 ; resistance, 541, 542 ; staphy- 
lolysin, 435, 539, 542, 547 ; symbiosis with Ameba 
coli, 687 ; symbiosis with B. influenza?, 564 ; toxicity 
of culture filtrates, 539, 540 ; toxin, soluble, 542 ; 
vaccination against, 548 ; varieties, 540, 541 ; viru- 
lence, 543. 

Staphylolysin ; see Staphylococcus. 

Stegomyia fasciata and its relation to yellow fever.... 713 

Streptococci in scarlet fever 26, 520, 523, 527 

Streptococcus brevis > 516 

Streptococcus erysipelatis 516 

Streptococcus longus 516 

Streptococcus mucosus capsulatus 516 

Streptococcus pyogenes 517-537 

Agglutination, 206, 536, 537 ; animals, susceptibility 
of, 518 ; antagonism for B. anthracis, 494, 528 ; for B. 
tuberculosis, 522 ; antistreptococcus serum, properties 
of, 529, 535 ; antistreptolysin, 519 ; Coley's mixture, 
529 ; cultivation. 517 ; in diphtheria, 401, 524 ; discov- 
ery, 515 ; endotoxin, 518 ; ervsipelas, 515, 520, 521 ; 
immunity, 316, 529, 530, 531 ; infection atria, 524 : in- 
fections, miscellaneous, 520. 529 ; in influenza, 567 ; 
leucocytes and leucocytosis, 530, 531 ; in meningitis, 

520, 557 ; in milk, 523 ; morphology, 515 ; opsonins. 
531 ; phagocytosis, 530, 531 ; in pneumonia, 501, 
510, 520, 521, 522 ; resemblance to pneumococcus, 
503 ; resistance, 517 ; in rheumatic fever, 520 359 ; 
in scarlet fever, 26, 520, 521, 533 ; serotherapy. 
534-536 ; serums, univalent and polyvalent, 533 ; 
streptocolysin, 519, 520 ; symbiosis with B. influ- 
enzae, 564 ; tissue reactions, 144 ; toxic properties, 
519, 520, 529 ; toxin for erythrocytes ; see Strepto- 
colysin ; toxin for leucocytes, 519 ; in tuberculosis, 

521, 522, 591, 592 ; tumors, influence on, 529 ; in 
typhoid fever, 439 ; unity, question of, 532 ; varie- 
ties, 516 ; virulence, 518. 

Streptococcus scarlatina? 527 

Streptocolysin 519, 520 

Streptothrix, infections with 634 

Streptotlirix maclurcc 634 



782 INDEX. 

PACK 

Subetam < 8< r»«tfbMi«atric< 262, 363 

Bummer diarrheas; Bee Dysentery, acute epidemic. 

Surra : Bee Trypanosomiasis In animals <*>m 

Susceptibility ISO, 158, 159 

i be individual disease -. 
Symptomatic anthrax. 
Antitoxin. 203; vaccination against, 363. 

Syncytlolysin 301 

Synonyms 863 

Syn toxoids r.»<;, :;."»:; 

Syphilis 25, 646, 652 

Animals, non-susceptibility of, 646; bacillus of De 
Lisle and Julien, 646; bacillus of Joseph nnd 
Piorkowski, 646; bacillus of Lustgarten, 646; Colle's 
law, »'.."■ l ; Immunity and susceptibility, 158, 651; 
Inheritance, 651 ; micro-organisms found in. 646; 
monkeys, transmission to, 648; other animals, trans- 
mission i". 649; Profetas law In. » *. ."• i ; reinfection, 
650, 651; Spirochete pallida In. 644; transmission, 
virulence, variations In, 650; virus, distribu- 
tion of, 650; virus, oon-fllterabllity of, 650; Was- 
sermann test In, 28 1. 

Tetanolysln 113, ii i 

Antitetanolysln, 367; neutralisation bj cholestrln, 204. 

Tetanospasmln 4 I 8, 1 1 I 

Tetanus 25, »" v 119 

tination reaction, 419; animal-, susceptibility of, 
156; cerebral, 415; <iir; and necrotic tissue, influence 
ill; dolorosa, US : excretion of toxin. 414 : 
Fourth of July, 412, 416 i "head tetanus,'' 1 14 ; 
in bones, 116; Immunity and susceptibility, 129, 
169. 316, 418, 415; "idiopathic," 412; Incubation 
period, 412 ; leu< • isorpl Ion of toxin, 1 18 : 

local, 415; mixed Infections, 31, 411, 412; nervous 
tissue, in fixation and transport of toxin, 414; 
occurrence of bacillus In the body, \\-\ occur- 
rence "i" i-.xin in the body, 413; pathogei 
413, 414; phagocytosis in, 315, 411: puerperal, 
■lit,; rheumaticus, 4 tj : seasons in relation t<» prev- 
alence, 412; Berotherapy ami prophylaxis, 866, 416, 
418; toxin (see />'. tetani, t<»xin of); treatment of 
wounds, 416; Wassermann's experiment, 414; 
wounds favoring development of, Jin; gee BaciUua 

(> tmii. 

Texas fever 684-686 

Thrush «;:::» 

Organisms of, * 139 ; susceptibility t<>. «;4n : systemic 
Infections, 640. 

Thyrotoxic 303 

••Tick fever;" see "Spotted fever.' 

Timothy bacillus 014 

Toxins." 

Absorption of. 100; animal. 21, 428-431 : attenuation 
of, 181 ; bacterial, 21, 3TS ; see individual bacteria ; 
ehemotaxis, influence on, 315. 520, 539 : crotin, 427; 
degenerative changes in. 193, 353 ; endotoxins, 179 ; 
see individual bacteria ; gastric juice, destructive 
action, 141 ; haptophores of, 192, 353 ; see side-chain 
theory ; immunization with, 181, 304 ; incubation 
period of, 170. 415 ; intracellular ; see Endotoxins ; 
leucocidin, 539 ; leucocytes in absorption of, 147, 
321 ; modifications by age, 198 ; neutralization by 
antitoxins, 191, 344; pancreatic juice, destructive 



INDEX. 783 

PAGE 

action, 142 ; phallin. 428 ; of pollens, 426 ; precipi- 
tation of, 177 ; preparation, 177 ; properties of, 176. 
352 ; as receptors of, second order, 351 ; ricin, 427 ; 
robin, 427 ; secondary or adventitious, 178 ; toxin 
spectrum, 194, 353 ; standardization of, 183 ; staph- 
ylolysin, 538 ; structure, 191 ; toxophores, 193, 353 ; 
see side-chain theory ; union with tissue cells, 177, 
200, 344, 348, 366, 368, 415; vegetable, 21, 425- 
428 ; see individual micro-organisms. 

Toxoids 193-196, 353 

Toxon 195, 35, 406 

Toxophorous group, toxophore 193, 351 

Trichomonas intestinalis, morphology and pathogenicitv 

of ." 693, 694 

Trichomonas vaginalis 693 

Trichophyton 640 

Tritotoxin 196, 353 

Trypanosoma 670 

Agglutination of, 671 ; cultivation of, 679, 681 ; mor- 
phology of, 670 ; multiplication of, 671 ; rosette 
formation by, 671 ; sleeping sickness, 673 ; species 
of, 670, 671, 677; trypanosomatic fever, 673. 

Trypanosomatic fever 673 

Sleeping sickness, relation to, 673, 674 ; symptoms 
of, 674 ; trypanosomes in, 674. 

Trypanosomiasis 670-684 

Agglutination reactions, 684 ; immunity and suscepti- 
bility, 683 ; in man, 673-677 ; parasites, occurrence 
of in the blood, 678 ; serotherapy of, 684 ; "trypan- 
roth" in treatment of, 684 ; vaccination in, 683 ; 
see Sleeping sickness and Trypanosomatic fever. 

Trypanosomiasis in animals 678-683 

Dourine, 682 ; horses, cattle and mules. 680-683 ; mal 
de cederas, 682 ; nagana, 680 ; in rats, 679 ; surra, 
681 ; symptomatology, 678. 
"Trypanroth" in treatment of trypanosomiasis. .. .683, 684 
Tsetse flies, in transmission of trypanosomiasis ; see 
Trypanosomiasis. 

Tuberculin of Koch and others 363, 364, 578, 579, 580 

Dangers, errors and limitations in use, 601, 602 ; 
diagnostic use of, 599-603. 612 ; disturbances caused 
by, 599 ; immunization with, 577, 598, 599 ; prepa- 
ration of. 578 ; principles of action. 606 ; specificity 
of. 601, 602 ; standardization of, 578, 580 ; therapy, 
602, 603. 

Tuberculocidin 580 

Tuberculosis 25, 573-615 

Agglutination as an index of immunity to, 607 ; ag- 
glutination reaction, 607, 610 ; amyloid degeneration 
in, 591 ; "anatomic tubercle," 585 ; in animals, 593, 
611 ; avian. 612; bovine, 611 ; bovine, relation of, to 
human, 582, 583 ; congenital, 584 ; disinfection in, 
593 ; dissemination by means of phagocytes, 588 ; 
"droplet infection," 585 ; "dust infection,' 585 ; 
healing, spontaneous, 587 ; heredity in, 596 ; immu- 
nity and susceptibility. 128, 130, 169, 593, 597, 599, 
607 ; immunization, mixed, 609 ; infection atria, 585, 
586 ; infectiveness of, 573 ; latent, 584 ; lupus vul- 
garis, 585 ; metastases in, 586 ; miliary, 587 ; mixed 
infections in. 591 ; organs attacked, 585, 586 ; pha- 
gocytosis, 588 ; pneumonia during, 510 ; predispos- 
ing factors to. 595 ; primary and secondary. 587 ; 
prophylaxis, 592, 593 ; pulmonary, 585 ; sero- 



784 INDEX. 

l'AGB 

therapy, 502, 808; Btreptococcua In, 520, 522; tis- 
sue changes In. 20, 588, 501 : tuberculin in 
diagnosis. 500, ''-"7 ; ulcerative, 585; vaccination 
against, 809 

Tumors, Influence of Btreptococcua on 529 

Turtle poison, antitoxin for 208 

Typhoid fever 25, 133 1 19 

Agglutination reaction, 23 200, 148, 440; antibodies, 
origin of, 320: baclllemia, ■»::: ; bacilli, distribution 
in the body, 437, 438 : blood cultures for diagnoaia, 
it'.': "duet" Infection, 438, 137; epidemiology 
of, 435; flies as carrlera, 436: Immunity and bub- 
ceptibiUty, 181, 187, 189. 439; Infection atrium, 
i.'T : leucocytes, 439. 442; leucotoxin In experi- 
mental Infections, 298; mixed Immunisation, 378 : 
inixcti Infections in. 439 •. prophylaxis, 442; Berum 
properties, 182; aerum prophylaxis, 443; serother- 
apy, berapy, active Immunisation, 448; 
therapy of Jea, iiT; vaccines and vaccination, 168, 
882, 1 13, 1 16 : see B. typhosus. 

typhus fever 25, 725 i 28 

Conditions for development, '-*'< : contagiousness, 726; 

endemics "i". ~-~> : Immunity In, Ti'T ; mlcr *gan- 

lams in. 727; occurrence, 725; transmission t" ani- 
mals, Tl'T : transmission i»v lice, 7^7. 

Ultramlcroscoplc micro-organisms 27 

i 'ndulanl f< ' i i Ita fever. 

Univalent Berums 

l'r< ase 208 

aatlon 5, 165, 862 364, 376 380 

Antibodies produced by, -".tt ; duration of resistance 

caused by. .':7»; : Incubation period, relation to, 378; 

Smalfpoi .i ii<i Bydrophobia; •'positive" and 

a tive phases," •■'•7 7; Bubstances osed for, 362- 

36 » : Bee the Individual dia 

Vaccines 362-864, 376-380 

the individual disi 

Vaccinia ; see Smallpox and Vaccinia. 

Varicella ; Bee < Jhickenpox. 

Variola Inoculata 7.; t 

Variola ; Bee smallpox. 

Venoms l. 177. 191, 198, 273-275, i> i:;i 

Amboceptors and complements, 273, 274, 430; and- 
renins, 174, 430, 4:: l ; character of, from different 
Bnake8, 4ir.» : cobralecithld, -7.". 429; cytotoxina of, 
4i".": endocomplementa for, -74. 430; endothelio- 
toxin of, 428; ferments >>\\ 4U'.t ; hemagglutinins of, 
428; hemolysin of, l'7:;. 428; bemorrhagln, 273, 
4i> : incubation period, 177. 4::i : lecithin as com- 
plement, -74. 4.".<>; neurotoxin of. 27.".. 4i> : radium, 
effed of, 4::i ; Btructure of cytotoxina of, 4U'.» : tox- 
ins of. 273; toxoids of. 428. 

Vibrio < huh in . 
Acquired immunity to. 310 ; action of gastric juice on, 
141 : active immunity, formation of specific precipi- 
tin in. 47'.i : agglutination of. by normal serum. 206; 
agglutination of. 4S0 ; agglutinins. 200 : attenuation 
of. 161 : autolytic products, vaccination with, 478 ; 
discovery. 469'; endotoxin of, 475; identification of, 
by agglutination reaction and by Pfeiffer experi- 
ment. 471 ; in Pfeiffer's phenomenon, 247 : in stools 
of convalescents, 472 ; location in infected body, 
47." ; morphology, staining properties and cultiva- 



INDEX. 785 

PAGE 

tion of, 470, 471 ; non-neutralization of endotoxin of, 
by its specific bactericidal serum, 253 ; occurrence 
of water, 472 ; resistance and viability of, 471 ; see 
Cholera; symbiosis with Ameba coli, 688; soluble 
toxin, 475 ; specificity of, 24 ; toxicity of culture 
filtrates, 475 ; toxicity of killed cultures, 475. 

Vibrio metchnikovi 10 

Virulence 88 

Increase of, in the presence of other micro-organisms, 
31 ; influence of, on inflammatory reaction, 144 ; 
relation of, to phagocytosis, 315 ; specialization of, 
89 ; see different micro-organisms. 

Virulin 121, 338 

Wasp Poison, antitoxin for 203 

Wassermann reaction 284 

Antigen in, 285 ; technic, 286 ; value of, 290 ; in non- 
syphilitic diseases, 291. 

Whooping cough (pertussis) 750-755 

Contagiousness, 753, 754 ; cultural characteristics and 
pathogenicity of the influenza-like bacilli, 751 : 
immunity and susceptibility, 754 ; influenza-like 
bacillus in, 751 ; influenza-like bacillus, relation to 
whooping cough, 753 ; Micrococcus catarrhaUs in, 
550 ; micro-organisms in, 750 ; prophylaxis, 754 ; 
pseudoinfluenza bacilli in, 565 ; serotherapy, 754 ; 
virus, dissemination of, 753. 
"Water-borne" epidemics; cholera, dysentery, typhoid. 

435, 457, 473 

Welch, hypothesis of 332 

Widal reaction 206, 225 

See Agglutination. 
Wool-sorters' disease ; see Anthrax. 
Wright's method of vaccination. 

Staphylococcus infections, 548 ; tvphoid fever, 443, 
444. 

Yellow fever 25, 711-720 

Acclimatization, question of, 719 ; altitude and mois- 
ture, relation to, 715 ; Bacillus icteroides in, 712, 
713 ; cold, relation to, 715 ; epidemiology, 715 ; 
fomites, 714, 715 ; immunity, acquired, 714, 720 ; 
importation by ships, 718 ; incubation period, 714 ; 
mosquito theory of, 712; se also Stegomyia fasciata; 
non-contagiousness of, 715 ; occurrence, 711 ; pro- 
phylaxis and quarantine of, 715, 716, 718, 719 ; 
virus, filterability of, 714 ; virus, resistance of, 
718 ; serotherapy, 720 ; susceptibility to, 719. 

Zooprecipitins 235 

Zootoxins 431 

Zivischenkbrper, synonyms for 263 

Zymotoxic groups 222 















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